Allocating registers on a spatial light modulator

ABSTRACT

Described is a device comprising: an array of light modulating elements; and one or more processing elements for controlling each of the light modulating elements, wherein the light modulating elements are arranged in a two-dimensional array, and wherein the one or more processing elements are adapted to skip some bit locations and use other bit locations of bit values when performing multiple bit logical and/or arithmetic operations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/457,864, filed Apr. 27, 2012, which is a divisional of U.S.application Ser. No. 11/382,818, filed May 11, 2006, entitled“Allocating Memory on a Spatial Light Modulator” (now U.S. Pat. No.8,189,015, issued May 29, 2012), which is a divisional of U.S.application Ser. No. 10/849,195, filed May 20, 2004, entitled “DigitalBackplane” (now U.S. Pat. No. 7,071,908, issued Jul. 4, 2006), which inturn claims priority from U.S. Provisional Patent Application No.60/471,731, entitled “Digital Backplane,” filed May 20, 2003, and U.S.Provisional Patent Application No. 60/568,253, entitled “RecursiveFeedback Digital Backplane,” filed May 6, 2004. The entire disclosureand contents of the above-identified U.S. patent, U.S. patentapplication and U.S. Provisional Application are incorporated herein byreference.

BACKGROUND

1. Field of the Invention

The present invention relates to a digital backplane and variousmethods, systems and devices for controlling a digital backplane, lightmodulating elements and spatial light modulators.

2. Related Art

The concept of digital LCoS devices has been known for well over 10years. The U.S. Pat. No. 5,959,598 to McKnight gives an example of manyof the basic digital LCoS concepts and is included herein by reference.U.S. Pat. No. 6,650,138 to Zuravleff shows another variation of this“master-slave” mirror drive arrangement. Both of these patents use afeed forward drive method. Both of these patents show a two-storage-bitstructure in which one of the storage bits is directly shifted to thenext bit for display and thus the two bits of storage are inexorablylinked together and connected to a specific output. However, the methodsdescribed in these patents require considerable bandwidth.

U.S. Published Patent Application Document No. 2003/0160803 to Willisshows a spatial light modulator microdisplay which uses a “feed forward”drive method. In this application, an N-bit pixel value is compared to aN-bit counter and the result of that comparison is used to drive adisplay mirror of an LCoS device. Willis shows an N-bit wide comparisonoccurring 2^(N) times in order to control the bit with each comparisonrequiring all N-bits. Willis shows needing at least N-bits of memorystorage on the display device to affect the PWM control. This means thatN-bits must somehow be sent/connect to an N-bit wide comparator 2^(N)times in order to control the PWM waveform.

SUMMARY

It is one object of the present invention to use recursive feedback todrive an LCoS device using a minimal amount of bandwidth.

It is a further object of the present invention to avoid requiring amulti-bit wide comparison to control an output.

It is yet a further object of the present invention to use fewer thanN-Bits on one or more comparisons to reduce the need to fetch data.

It is yet a further object of the present invention to use significantlyfewer than 2^(N) comparisons to determine a PWM waveform with 2^(N)different widths.

According to a first broad aspect of the present invention, there isprovided a device comprising: electrode means comprising at least oneelectrode for controlling a light modulating element of an array oflight modulating elements; and recursive feedback control means forcontrolling at least one pulse width using recursive feedback, the pulsewidth driving the electrode means.

According to a second broad aspect of present invention, there isprovided a method comprising the following steps: (a) controlling atleast one pulse width using recursive feedback; and (b) driving anelectrode means using the pulse width to thereby control a lightmodulating element of an array of light modulating elements.

According to a third broad aspect of present invention, there isprovided a system comprising: means for controlling at least one pulsewidth using recursive feedback; and means for driving an electrode meansusing the pulse width to thereby control a light modulating element ofan array of light modulating elements.

According to a fourth broad aspect of present invention, there isprovided a device comprising: an array of storage bits for controllingan array of outputs; and updating means for conditionally updating thestorage bits.

According to a fifth broad aspect of present invention, there isprovided a method comprising: forming a plurality of single pulses byperforming two series of count steps for each of the plurality of singlepulses, and controlling an array of light modulating elements using arespective single pulse of the plurality of single pulses for each lightmodulating element of the array.

According to a sixth broad aspect of present invention, there isprovided a system comprising: means for forming a plurality of singlepulses by performing two series of count steps for each of the pluralityof single pulses, and means for controlling an array of light modulatingelements using a respective single pulse of the plurality of singlepulses for each light modulating element of the array.

According to a seventh broad aspect of present invention, there isprovided a device comprising: an array of light modulating elements; andmeans for generating pulse widths for each of the light modulatingelements using bit serial processing.

According to an eighth broad aspect of present invention, there isprovided a method comprising: providing an array of light modulatingelements; and generating pulse widths for each of the light modulatingelements using bit serial processing.

According to a ninth broad aspect of present invention, there isprovided a system comprising: an array of light modulating elements; andmeans for generating pulse widths for each of the light modulatingelements using bit serial processing.

According to a tenth broad aspect of present invention, there isprovided a device comprising: a substrate; an array of electrodes forcontrolling light modulating elements, the electrodes being located onthe substrate; and an array of bit serial processing elements forcontrolling the light modulating elements, the bit processing elementsbeing located on the substrate.

According to an eleventh broad aspect of present invention, there isprovided a device comprising: a two-dimensional array of lightmodulating elements; output bits for controlling each of the lightmodulating elements; reading means for reading one bit position of pixelvalues for a one-dimensional array of light modulating elements of thetwo-dimensional array of light modulating elements; and means forcomputing a one-dimensional array of control signals for the output bitsbased on one or more sets one-bit positions of the pixel values, whereinthe control signals are capable of being used to control a next value ofeach of the output bits to thereby control each of the light modulatingelements.

According to a twelfth broad aspect of present invention, there isprovided a method comprising the following steps: (a) inputtingpartially or fully encoded pixel values for an array of light modulatingelements using digital processing to convert the pixel values to pulsewidths; and (b) controlling a plurality of light modulating elements ofthe array of light modulating elements using a series of instructions tocontrol multiple data path elements.

According to a thirteenth broad aspect of present invention, there isprovided a system comprising: means inputting partially or fully encodedpixel values for an array of light modulating elements using digitalprocessing to convert the pixel values to pulse widths; and means forcontrolling a plurality of light modulating elements of the array oflight modulating elements using a series of instructions to controlmultiple data path elements.

According to a fourteenth broad aspect of present invention, there isprovided a method comprising: controlling at least one pulse width usinga recursive feedback process; and controlling an array of electrodesusing the at least one pulse width, wherein the recursive feedbackprocess is performed using bit serial processing.

According to a fifteenth broad aspect of present invention, there isprovided a system comprising: means controlling at least one pulse widthusing a recursive feedback process; and means for controlling an arrayof electrodes using the at least one pulse width, wherein the recursivefeedback process is performed using bit serial processing.

According to a sixteenth broad aspect of present invention, there isprovided a method comprising the following steps: (a) providingavailable memory on a spatial light modulator; and (b) reallocating theavailable memory for data on the spatial light modulator, wherein spaceallocated is based on the length of time that the data needs to stayresident on the spatial light modulator and wherein the data isprocessed to control electrodes on the spatial light modulator.

According to a seventeenth broad aspect of present invention, there isprovided a system comprising: means for providing available memory on aspatial light modulator; and means for reallocating the available memoryfor data on the spatial light modulator, wherein space allocated isbased on the length of time that the data needs to stay resident on thespatial light modulator and wherein the data is processed to controlelectrodes on the spatial light modulator.

According to an eighteenth broad aspect of present invention, there isprovided a device comprising: a backplane comprising an instructionmemory for holding instructions for controlling at least one pulse widthon each light modulating element of a spatial light modulator.

According to a nineteenth broad aspect of present invention, there isprovided a device comprising: a backplane for a spatial modulator; aplurality of pointers to bit position array on the backplane; andpointer controller means for controlling the plurality of pointers.

According to a twentieth broad aspect of present invention, there isprovided a method comprising: storing a first group of bit positions ofa plurality of pixels in bit position arrays on a backplane, the firstgroup of bit positions comprising a contiguous group of bit positions;storing at least one second group of bit positions on the backplane, thesecond group of bit positions corresponding to a subset of the pluralityof pixels; and combining on the backplane the first group and the atleast one second group to thereby control a pulse width of one or morelight modulating elements, wherein the second group of bit positions isstored for a shorter period of time on the backplane than the firstgroup of bit positions is stored on the backplane.

According to a twenty-first broad aspect of present invention, there isprovided a system comprising: means for storing a first group of bitpositions of a plurality of pixels in bit position arrays on abackplane, the first group of bit positions comprising a contiguousgroup of bit positions; means for storing at least one second group ofbit positions on the backplane, the second group of bit positionscorresponding to a subset of the plurality of pixels; and means forcombining on the backplane the first group and the at least one secondgroup to thereby control a pulse width of one or more light modulatingelements, wherein the second group of bit positions is stored for ashorter period of time on the backplane than the first group of bitpositions is stored on the backplane.

According to a twenty-second broad aspect of present invention, there isprovided a method comprising: storing a first group of bit positions ofa plurality of pixels in bit position arrays on a backplane, the firstgroup of bit positions comprising a contiguous group of bit positions;storing at least one summary bit of the plurality of pixel value on thebackplane, and combining on the backplane the first group and the atleast one summary bit to thereby control a pulse width of one or morelight modulating elements, wherein the summary bit is stored for ashorter period of time on the backplane than the first group of bitpositions is stored on the backplane.

According to a twenty-third broad aspect of present invention, there isprovided a system comprising: means for storing a first group of bitpositions of a plurality of pixels in bit position arrays on abackplane, the first group of bit positions comprising a contiguousgroup of bit positions; means for storing at least one summary bit ofthe plurality of pixel value on the backplane, and means for combiningon the backplane the first group and the at least one summary bit tothereby control a pulse width of one or more light modulating elements,wherein the summary bit is stored for a shorter period of time on thebackplane than the first group of bit positions is stored on thebackplane.

According to a twenty-fourth broad aspect of present invention, there isprovided a device comprising: an array of circuits comprising: means forvoltage level shifting; a selectable logic function based on a memorybit; and means for controlling one or more light modulating elements,wherein a constant voltage source is used for the array of circuits.

According to a twenty-fifth broad aspect of present invention, there isprovided a method comprising: determining a pulse wave form for eachline of a two-dimensional array of drive bits using a recursive feedbackprocess, wherein each drive bit in the array of drive bits is in aninitialized state; and turning all of the drive bits to an off state tothereby produce a blanking interval between fields for an image, whereincontrol of each of the pulse wave forms is staggered in time.

According to a twenty-sixth broad aspect of present invention, there isprovided a system comprising: means for determining a pulse wave formfor each line of a two-dimensional array of drive bits using a recursivefeedback process, wherein each drive bit in the array of drive bits isin an initialized state; and means for turning all of the drive bits toan off state to thereby produce a blanking interval between fields foran image, wherein control of each of the pulse wave forms is staggeredin time.

According to a twenty-seventh broad aspect of present invention, thereis provided a device comprising: a spatial light modulator comprising anarray of master-slave bit pairs, wherein for each master-slave bit paira master bit includes means for selectively driving a correspondingslave bit, and wherein both the master bit and the corresponding slavebit are capable of being randomly accessed.

According to a twenty-eighth broad aspect of present invention, there isprovided a method comprising: providing an m bit input pixel value; andmapping the m bit input pixel value into a non-binary weighted singlepulse using time based remapping to thereby control a light modulatingelement of a spatial light modulator.

According to a twenty-ninth broad aspect of present invention, there isprovided a system comprising: means for providing an m bit input pixelvalue; and means for mapping the m bit input pixel value into anon-binary weighted single pulse using time based remapping to therebycontrol a light modulating element of a spatial light modulator.

According to a thirtieth broad aspect of present invention, there isprovided a device comprising: a backplane controller including means forsequencing a series of instructions, wherein the instructions controlmemory accesses to data that is used to control one or more pulse widthson a spatial light modulator.

According to a thirty-first broad aspect of present invention, there isprovided a method comprising: mapping an input pixel value for eachpixel of an array of pixels to a first output pixel value using a firsttime base to generate first pulse width; and mapping the input pixelvalue to a second output pixel value using a second time base togenerate a second pulse width to thereby reduce the worst case phasedifference in adjacent pixels of a spatial light modulator, wherein theadjacent pixels of the array of pixels have respective input pixelvalues that differ by 1 LS-bit.

According to a thirty-second broad aspect of present invention, there isprovided a system comprising: means for mapping an input pixel value foreach pixel of an array of pixels to a first output pixel value using afirst time base to generate first pulse width; and means for mapping theinput pixel value to a second output pixel value using a second timebase to generate a second pulse width to thereby reduce the worst casephase difference in adjacent pixels of a spatial light modulator,wherein the adjacent pixels of the array of pixels have respective inputpixel values that differ by 1 LS-bit.

According to a thirty-third broad aspect of present invention, there isprovided a device comprising: an MRAM array of MRAM storage bits for aspatial light modulator, the MRAM storage bits being arranged in MRAMcolumns; and bit lines for each of the MRAM columns, wherein the bitlines support a first and a second driver on opposite sides of thearray, wherein the MRAM storage bits are for a spatial light modulator.

According to a thirty-fourth broad aspect of present invention, there isprovided a device comprising: an array of drive bits; and means forperforming a masked write to the drive bits.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flow chart illustrating a prior feed forward controlprocess;

FIG. 2 is a flow chart illustrating a recursive feedback control processin accordance with one embodiment of the present invention;

FIG. 3 is a table outlining a recursive feedback method in accordancewith one embodiment of the present invention;

FIG. 4 is a simplified timing diagram for the control method shown inthe table of FIG. 3;

FIG. 5 is a diagram in simplified form illustrating a circuit employingexplicit recursive feedback;

FIG. 6 is a diagram in simplified form illustrating a circuit that isfunctionally equivalent of the circuit in FIG. 5 for many purposes thatemploys implicit recursive feedback;

FIG. 7 shows an SRAM bit connected to a mirror;

FIG. 8 shows a logical representation of a simplified 2 row by 2 columnSRAM;

FIG. 9 shows a 2 row by 2 column array that demonstrates a simplifiedwrite mask SRAM design in accordance with one embodiment of the presentinvention;

FIG. 10 is a diagram showing a dual counting with deduction process inaccordance with an embodiment of the present invention;

FIG. 11A illustrates in simplified form a memory array circuit inaccordance with an embodiment of the present invention;

FIG. 11B illustrates in expanded form a set of components of the memoryarray of FIG. 11A for a single mirror/electrode;

FIG. 12 illustrates in simplified form a 1-bit wide “slice” of MRAM andERAM input and output buffers and a processing element (PE) thatsupports one embodiment of the present invention;

FIG. 13 illustrates in simplified form a 1-bit wide “slice” of MRAM andERAM input and output buffers and a processing element (PE) thatsupports one embodiment of the present invention;

FIG. 14 is a simplified diagram of a PE functionality of the presentinvention;

FIG. 15 shows an alternative implementation of an ERAM storage bit thatsupports computation within a memory in accordance with one embodimentof the present invention;

FIG. 16 is a high level block diagram of one embodiment of a digitalbackplane 2402 of the present invention

FIG. 17 is a simplified high level block diagram of a digital backplanein accordance one embodiment of the present invention;

FIG. 18 is a table illustrating a simplified example of a backplanecontrol processing sequencing according to one embodiment of the presentinvention;

FIG. 19 is a table illustrating a simplified example of a backplanecontrol processing sequencing according to one embodiment of the presentinvention;

FIG. 20 is a table illustrating a simplified example of a backplanecontrol processing sequencing according to one embodiment of the presentinvention;

FIG. 21 is a table illustrating a simplified example of a backplanecontrol processing sequencing according to one embodiment of the presentinvention;

FIG. 22 is a high level block diagram showing a system employing a panelbackplane in accordance with one embodiment of the present invention;

FIG. 23 is a high level block diagram showing another system employing apanel backplane in accordance with one embodiment of the presentinvention;

FIG. 24 is a high level block diagram showing another system employing apanel backplane in accordance with one embodiment of the presentinvention;

FIG. 25 is a table providing an example of how summary bits areproduced;

FIG. 26 is a simplified diagram of a backplane controller according toone embodiment of the present invention;

FIG. 27 is a table illustrating simplified example of a method to changethe time base between fields to break up transitions that cause theworst case “out of phase” lateral fields in a smoothly ramping (steppingby 1) image;

FIG. 28 is a timing diagram illustrating the phase differences betweenusing two different time bases combined with two different table lookupre-mappings of the input pixel values;

FIG. 29 is a diagram showing a bit cell with inverting level shifter inaccordance with an embodiment of the present invention;

FIG. 30 is a diagram showing an another bit cell with inverting levelshifter in accordance with an embodiment of the present invention;

FIG. 31 is a diagram showing a bit cell that supports both levelshifting and a multiple logic functions in accordance with an embodimentof the present invention; and

FIG. 32 is a memory map illustrating multiple circular buffers for usewith a digital backplane of the present invention.

FIG. 33 is a simplified schematic diagram showing a bit serial processorcontrolling light modulating elements of a spatial light modulator of avisual display device in accordance with one embodiment of the presentinvention.

DETAILED DESCRIPTION

It is advantageous to define several terms before describing theinvention. It should be appreciated that the following definitions areused throughout this application.

DEFINITIONS

Where the definition of terms departs from the commonly used meaning ofthe term, applicant intends to utilize the definitions provided below,unless specifically indicated.

For the purposes of the present invention, a value or property is“based” on a particular value, property, the satisfaction of acondition, or other factor, if that value is derived by performing amathematical calculation or logical decision using that value, propertyor other factor. For example, a “next output value” may be based on a“current output value”, a line of an SRAM may be pulled down, or not,based on the output bit of an inverter, etc. In the context of thepresent invention, it should be understood that some storage structureand/or memory circuits will support a new value being based on its oldvalue without having to physically read or write the bit to logic formaking the calculation or decision, and in this case the feedback isconsidered to be “implicit” feedback.

For the purposes of the present invention, the term “array of storagebits” refers to a memory.

For the purposes of the present invention, the term “available memory”refers to memory on a device that is not currently needed by some otherprocess performed by the device.

For the purposes of the present invention, the term “backplane” refersto a substrate that is used to build logic and control functions for adisplay device. A backplane may be made of a semiconductor material,such as silicon, GaAs, etc. and it would include transistors that aredeposited or grown on a substrate such the well-known formation oftransistors on a glass or other insulating substrate.

For the purposes of the present invention, the term “binary weighted oftime” refers to means that successively higher bit positions in apixel's value represent a doubling of time. Thus for example if bitposition 0 (the least significant bit position) represents an amount oftime T, then bit position 1 will be 2T long, bit position 2 will be 4Tlong, and so forth.

For the purposes of the present invention, the term “bit plane buffer”refers to storing all or part of a bit plane in a physical memorylocation. A bit plane buffer, may or may not store the bit plane in thesame array order as it is seen in a visual display. In some embodimentsof the present invention, the ERAM will store one or more bit planebuffers. In some embodiments these bit plane buffers will be alsocircular buffers.

For the purposes of the present invention, the term “bit plane” refersto taking on bit position from an array of pixels to form a bit arraythat is of the same dimensions as pixel array but with only one bit perelement of the array. A “bit plane” may be either physically separatedin the case of “bit-plane organized” data or it may be used to refer tothe concept of a bit position within an array of pixels. A “bit plane”may also be an array of bits that correspond to an array of pixels andthe bit value may be based on some computation of the original pixel. Insome embodiments a series of “summary bits” is generated that may betreated as a bit plane.

For the purposes of the present invention, the term “bit position”refers to a bit location within an ordered group of bits.

For the purposes of the present invention, the term “bit recursivefeedback” refers to using a single bit of storage at or near the outputor a duplicate copy thereof as a one bit input to help form the nextoutput.

For the purposes of the present invention, the term “bit recursivefeedback” refers to recursive feedback where the value being fed back isa single bit. The feedback may be either a signal, a memory read, or asis the case of some embodiments of the present invention, an implicitfeedback where the next state of the bit is based on the previous statewithout having to physically read or feedback the old value.

For the purposes of the present invention, the term “bit serialprocessing” refers to a method where a multi-bit computation isperformed as a series of one-bit wide operations where the result(s)from previous operations may be used as inputs to the next operation.Bit serial processing may store each bit of precision at a differentmemory address. To control the massive number of outputs using bitserial processing a technique known as Single Instruction, Multiple DataStream (SIMD) processing may be employed.

For the purposes of the present invention, the term “bit serialprocessor” refers to a device that carries out bit serial processing.

For the purposes of the present invention, the term “bit serialprocessing element” or “bit serial PE” refers to the data processingportion of a bit serial processor.

For the purposes of the present invention, the term “bit-parallel SIMD”refers to SIMD processors that have data paths that operate on multiplebits per cycle. Examples of bit-parallel SIMD processors are describedand shown in U.S. Pat. Nos. 4,773,038 and 5,864,703, the entire contentsand disclosures of which are hereby incorporated by reference.

For the purposes of the present invention, the term “bit-plane organizeddata” refers storing each bit position of an array of pixels (each bitplane) in a physically separate location. For simplicity of writing whenit is clear that the reference is to bit-planned organized data, thesewill simply be referred to as “bit planes.”

For the purposes of the present invention, the term “bit-position array”refers to a subset of the bit positions for a group of pixels.

For the purposes of the present invention, the term “bits/sec/pin”refers to bits per second per pin and is the metric that may be used togive the speed of the bus. For Double data Rate Synchronous DRAM (DDRAM)busses bit/sec/pin is twice the clock rate.

For the purposes of the present invention, the term “bit-serial SIMD”refers to SIMD processors that have one bit wide data paths within thePEs. In their simplest form bit-serial SIMD processors work on one bitof precision per cycle. Examples of bit-serial SIMD processors aredescribed and shown in U.S. Pat. Nos. 4,621,339; 5,210,826; 5,581,773and 6,493,467, the entire contents and disclosures of which are herebyincorporated by reference.

For the purposes of the present invention, the term “buffer” refers to adata storage structure where bits are saved temporarily. Often a bufferneeds to support bits going in and out at the same time and may be adual port RAM or some form of double buffering. One or more buffers mayalso be used to take in data bits at one width and data rate and outputthe data bits at a different rate and/or data width. The term “buffer”includes references to the temporary storage or delays of single bitvalues or control signals.

For the purposes of the present invention, the term “circular buffer”refers to a memory accessing method with a read pointer and a writepointer, wherein both the read and write pointer are reset to the top ofthe buffer if the pointers exceed the end of the buffer length. A memorypointer moves in a circular buffer fashion when the memory pointer isused to point to a circular buffer and the memory pointer is controlledso memory operations stay within the bounds of the circular buffer.

For the purposes of the present invention, the term “conditionallyupdating” refers to either “conditionally setting,” or “conditionallyresetting” a storage bit. The storage bit may be part of a memory array.“Conditionally updating” may be used interchangeably with the term“conditionally writing” for the purposes of the present invention. Atleast some common memories such as a conventional SRAM or Dynamic RAM(DRAM) only support unconditional writing that can only set a given bitto a 1 or a 0, regardless of its current state. A memory that supportscondition updating has the ability to control whether or not a given bitis written. A “masked write” is one implementation of a “conditionalupdate.” Conditionally resetting may also be referred to as“conditionally clearing.”

For the purposes of the present invention, the term “column” is usedwith respect to a memory organized bit lines. Often there are two bitlines per “column” of memory. Often there is a column decoder whichfunctions to multiplex a plurality columns to form a single output.Compared to most typical memory, there will be a large number of outputsmany of the on-backplane memories which will result in little or in somecase no column decoding.

For the purposes of the present invention, the term “contiguous bitpositions” refers to bit positions that have sequential weighting. Whatit is most common for bits to be associated with a binary weighting, theweighting of the bits may be other than binary in terms of the way theyaffect the output of a spatial light modulator or the control thereof.

For the purposes of the present invention, the term “count stage” or“pulse stage” refers to the computations of whether a digitallycontrolled pulse width can go up or down at a finite number of points.The computations at each of these points are collectively referred to asa stage. There may be multiple clock cycles on the backplane andmultiple operations that go into computing whether the pulse goes up ordown for a given stage.

For the purposes of the present invention, the term “count step” refersto one step of a multi-step process where each step controls orpotentially controls a transition of a pulse high or low. A count stepmay be performed using in one or more cycles using an individual logicalor arithmetic operation or a series of logical or arithmetic operations.

For the purposes of the present invention, the term “current count”refers, conceptually, to the current position in a pulse width that isbeing determined. While the current count may be thought of as aphysical count or counter, the current count may just be a conceptualpoint in a sequencing device or program. In the case of one embodimentof the present invention there is no physical “count” but rather thereis a stage of a program that causes certain events so that the “physicalcount” and compare operation is replaced by a program sequence.

For the purposes of the present invention, the term “data cycles” to thetime it takes to transfer one bit of data on one data line. In the caseof some data busses such as those associated with “double data rate”such as DDRAM, the data is sampled on the leading and trailing edge of aclock cycle and thus making two “data cycles” for every clock cycle. Forthe purposes of the present invention, the rate at which data is sampledwill be call the data cycle.

For the purposes of the present invention, the term “dedicated panelframe buffer” or “dedicated backplane frame buffer” refers to a framebuffer that includes memory locations that only provide data on abackplane.

For the purposes of the present invention, the term “deductive pulsewidth control” refers to method for controlling a pulse wherein onlysome of the bits of a pixel's value bits need to be looked at on mostcycles. Such a deductive pulse width control may be made possible by therecursive feedback support. An example of deductive pulse width controlis described below with respect to FIGS. 3 and 4.

For the purposes of the present invention, the term “display element” isa general term to describe a single element of a multidimensionaldisplay. This element may be a small mirror in the case of LCoS or aDLP™ device, or it may be a single Light Emitting Diode (LED), or evenan element of a print out of from a printer.

For the purposes of the present invention, the term “drive output bit”or “drive bit” refers a storage bit that is used to drive an electrodethat controls an output, such as the output of a spatial lightmodulator. A drive bit is a storage bit upon which an output of a deviceis based, either directly or, through other circuitry, has an output ofthe device based on it. For example, a drive output bit may drive anelectrode through additional circuitry including logic circuitry andvoltage level shifting so that the electrode is based on the driveoutput bit. An output of a device may be purely visual such as thecontrol of reflected or emitted light. In some embodiments of thepresent invention, a reflective mirror is used both as an electrode andan optical mirror, while in other embodiments of the present invention,such as when electrodes drive LEDs, the electrodes may not also beoptical mirrors. An MRAM is a collection of drive output bits, as wellas possibly other storage bits organized into a memory array.

For the purposes of the present invention, the term “driving anelectrode” refers to driving an electrode either directly or throughother circuitry. The circuitry used in driving an electrode may includelogic functions.

For the purposes of the present invention, the term “explicit recursivefeedback” refers to a recursive feedback process wherein feedback signalor feedback data is based on a separate feedback signal or a memory readoperation.

For the purposes of the present invention, the term “feed forward”refers to computations that are made without feeding back results fromprior stages. A common feed forward function used in displays is tocompare a count to the value of pixel.

For the purposes of the present invention, the term “field sequentialcolor” refers to a visual display apparatus presenting in sequence thevarious colors required to form a color image. Often using a fastspinning color wheel with different color filters, the various colorsflash on the display device. With field sequential color, essentially asingle color illuminates the spatial light modulator at a time. Due tothe way the human visual system behaves, it has been found it requireshigher field rates to keep a person from perceiving an effect known ascolor breakup.

For the purposes of the present invention, the term “field sequentialcolor” with no pre-qualifiers refers to a spatial light modulator thatis illuminated by single color fields scrolling across a light modulatorsuch as would occur with a segmented rotating color wheel.

For the purposes of the present invention, the term “flashingsequential” refers to the situation where a spatial light modulator iseither illuminated by or generates a field without the light scrolling.This would be the case for example, if the spatial light modulator isilluminated by a series of LEDs in various colors where only one coloris turned on at a time. A flashing sequential display process may alsobe used for monochrome displays and/or constant illumination displays.

For the purposes of the present invention, the term “gamma correction”refers to mapping input pixel values to output pixel values. In displaydevices, it is common to not want a linear change in the input value tohave a linear response on the display. Additionally other displaycharacteristics are adjusted by the “gamma correction.”

For the purposes of the present invention, the term “heterogeneousbit-position array” refers to a bit-position array in which the bitpositions are more than one bit position.

For the purposes of the present invention, the term “homogeneousbit-position array” refers to a bit-position array in which all of thebit positions are only one bit position.

For the purposes of the present invention, the term “horizontal lines”is a term that is relative to the image as viewed. When describing adisplayed image, in the descriptions of the present invention below theterms vertical and horizontal lines are used. In the descriptions of thepresent invention below, the terms “columns” and “rows” refer to memorystructures. In some embodiments, the ROWs in the MRAM and/or ERAM mayrun in the same direction as the horizontal “lines” (as would typicallyoccur for example in a top to bottom raster scanning display) of theimage generated and in other embodiments the columns of the MRAM andERAM may run in the direction of the horizontal “line” (as in the caseof a “horizontal scanning” display).

For the purposes of the present invention, the term “implicit recursivefeedback” refers to a recursive feedback process in which the feedbackdata is not based on a separate feedback signal nor on a memory readoperation. Examples of implicit recursive feedback include an outputbased on a masked write operation, a set-reset type of storage function,a D flip-flop with an inhibited clocking means, etc.

For the purposes of the present invention, the term “implicit recursivefeedback” or simply “implicit feedback” refers to the situation where acurrent output value has an effect on the next output value but wherethe storage device for the output value is such that the bit does nothave to be physically read or wired out. An example of implicitrecursive feedback would be a set, reset flip flop. A set-reset flipflop may be set to a 1, or reset to a 0, or importantly, if neither aset nor reset signal is applied the state will remain the same. Thisoption for the bit to be optionally set, reset, or left alonefacilitates a form of virtual recursive feedback. In one embodiment ofthe present invention, a memory structure that uses ordinary RAM storagebits for high density but supports this ability with the column drivercircuitry to support a “masked write” will support this virtualrecursive feedback.

For the purposes of the present invention, the term “inherentlytestable” refers to a circuit or an array of circuits that may be testedwithout requiring the use of special test circuitry within each elementof the circuit or array of circuits. For example, an SRAM bit isinherently testable.

For the purposes of the present invention, the term “input pixel value”refers to the numerical value associated with a pixel before the valueis corrected or adjusted to compensate for the various system and deviceresponse characteristics.

For the purposes of the present invention, the term “instruction” isused to mean a set of control bits held at one or more addresses in oneor more memories that are used to control one or more data processingoperations as are common in stored program computers such as amicroprocessor or microcomputer. The memory that contains theinstructions is commonly referred to as the instruction memory. A seriesof addresses in the instruction memory cause a “series of instructions”to be fetched for use to control data processing. The sequencing ofinstructions may be controlled by a counter often known as a programcounter (PC) to fetch instructions in a numerical order by addresslocation and/or some form of conditional or unconditional jumping orbranching operation. The bits in an instruction may be used withoutdecoding to cause a given control action or often they are decoded, usedas addresses into a memory, or otherwise manipulated to generate thefinal control signals that act to give the processing action desired. Asis well known in the art, instructions can be held in random accessmemory (RAM) in which case they can be downloaded at any time, or theymay be “burned” onto ROM, Flash memory or other types of storage devicesthat don't require downloading once programmed and may or may not bereprogrammable.

For the purposes of the present invention, the term “intermediate outputbit” refers to an output bit that is not a drive output bit.

For the purposes of the present invention, the term “light modulatingelement” refers to a means for controlling the properties of a lightsource. For example, a light modulating element may control a lightemitting source such as an, phosphor dot, LED, etc., may control the waylight is reflected by a mirror device, may control the polarization oflight such as in an LCD device, etc.

For the purposes of the present invention, the term “liquid crystaldisplay device” or “LCD device” refers to the conventional meaning ofthe term LCD device as well as to related such as LCOS devices.

For the purposes of the present invention, the term “LS-bit time” refersto the time between two pulses differing by 1 in their least significantbit assuming “binary weighting” of time with respect to the bitspositions of a pixel. Alternatively it may mean for non-binary weightingof time the time if only the very least significant bit of a pixel is a1.

For the purposes of the present invention, the term “masked write”refers to a write operation in which some bit or group of bits isenabled or disabled from writing based on a separate mask value. In oneembodiment of the present invention, the masking is supported on abit-by-bit basis. In one embodiment of the present invention, the datawritten is common broadcasted in some operations and the control of theoutputs is based on whether various bits are enabled to be written. Thisin effect treats the storage bits as a “Set-Reset” (SR) flip flop, thatmay be set, reset, or left unmodified. A masked write is one way toimplement a conditional update. An example of a RAM with masked writecapability is shown in FIG. 9.

For the purposes of the present invention, the term “master-slave”refers to a two bit storage circuit wherein there in there is a “masterbit” that takes data in and then at some later time transfers it to a“slave bit.” Master-slave bits have been common in some forms of digitalbackplanes for LCoS. In prior digital LCoS devices using master-slavebits to control the mirror/electrode, only the “master bit” of amaster-slave bit pair may be randomly accessed and the “slave bit” willdrive the mirror/electrode. Some embodiments of the present inventionmay use master-slave bits in the memory array that includes the driverbits (the “MRAM array”) and other embodiments will not need or usemaster-slave bits for the driver bits. In some embodiments it may bedesirable to randomly access either the “master bit” or the “slave bit”were the slave bit is a driver bit and the master bit can at times beused as general purpose storage

For the purposes of the present invention, the term “microdisplays”refers to any of a class of display devices that are sufficiently smallto require some form of magnification for human viewing for theirintended use in a product.

For the purposes of the present invention, the term “mirror bit cell”refers to a device including a mirror bit and a mirror driven by themirror bit. A mirror bit cell may include other features such asinverters, bit lines, a row select, a DC balancing block 742, etc. Anexample of a mirror bit cell according to one embodiment of the presentinvention is shown in FIG. 7 and is described below.

For the purposes of the present invention, the term “mirror bit” refersto a drive bit used to drive a mirror. The output control bit of FIG. 2is an example of a mirror bit of the present invention. Another exampleof an output control bit of the present invention is the SRAM bit of themirror bit cell of FIG. 7.

For the purposes of the present invention, the terms “mirror” and“electrode” may each sometimes be used to refer to: a mirror driven byan electrode, an electrode that drives a mirror and/or the combinationof a mirror and the electrode that drives the mirror. For example, aphrase such as “controlling a mirror” may also refer to “controlling anelectrode that drives a mirror.”

For the purposes of the present invention, the term “MRAM bit” refers toa storage bit and any drive circuitry with the storage bit. For manypurposes of the present invention, the terms “MRAM bit” and “drive bit”may be used interchangeably. For example, when an MRAM bit is used todrive a mirror, the terms “MRAM bit” and “mirror bit” may be usedinterchangeably.

For the purposes of the present invention, the term “non-circularbuffer” refers to any memory accessing method that is not a circularbuffer.

For the purposes of the present invention, the term “ordered group ofbits” refers to a group bits wherein the position of each bit within thegroup of bits relates to a numerical value or other weighting such aslength of time associated with the bit. The bits of an ordered group ofbits may or may not be stored contiguously. For example, an orderedgroup of bits may have all the bits of one position for a number ofelements, such as pixels, stored in one area of memory and other bitpositions stored in other areas of memory. A pixel is an example of anordered group of bits.

For the purposes of the present invention, the term “output bit” refersto a logical storage device that stores the state of a logic circuit.The term output bit also refers to a mirror copy of an output bit, aninversion of an output bit, etc. In the case of a drive output bit ordrive bit, the mirror copy of the output bit may be an ordinary bitwithout the ability to drive an electrode based on the bit. It isanticipated that in some embodiments a mirror copy of the drive bit maybe used to compute the next state of a drive output bit using recursivefeedback.

For the purposes of the present invention, the term “output pixel value”refers to the numerical value of a pixel after any modifications to theinput pixel value to adjust for any system and device responses.

For the purposes of the present invention, the term “packed pixel” or“packed data” refers a way of storing an “ordered group of bits” wherein all the bits are store “packed” into a single location in memory. Forexample, an 8-bit packed pixel will be stored in a single 8-bit byte inmemory.

For the purposes of the present invention, the term “Panel Interface(PIF)” refers to a device that interfaces between, incoming video data,a DRAM or Double data Rate input DRAM (DDRAM) used for temporary storageor as an external data buffer.

For the purposes of the present invention, the term “panel” displaydevice including a backplane. In the case of LCoS, a panel may be formedfrom a backplane by forming a sealed chamber on top of the backplane andfilling the chamber with a liquid crystal material. The terms“backplane” and “panel” will be used interchangeably to refer to thespatial light modulator.

For the purposes of the present invention, the term “pixel electrode”refers to one or more electrical connections that drive a pixel. Forsome display devices only a single electrode will be driven, but forother devices it may be necessary to drive two or more electrodes toaffect the output, such as driving the true and complement value on twoelectrodes.

For the purposes of the present invention, the term “pixel value” refersto the numerical value associated with a pixel. When used without apre-qualifier as “input or output” a pixel value refers to the currentvalue of the pixel.

For the purposes of the present invention, the term “pixel” or “pictureelement” is a group of bits on which an element of a light modulator isbased. Conceptually, a series of pixels flows through a system and areprocessed in order to drive an element of the display. The term“physical pixel” will be used to refer to the physical/viewable outputin an array of light modulating output elements (the “dots” of adisplay). The output may be a spatial light modifier that affects theway light is reflected as with an LCoS display or a DLP™ display, or maybe used to drive a light emitting devices such as and LED. The value ofthe “pixel” may be modified and the number of bits in the grouprepresented by the pixel may be modified.

For the purposes of the present invention, the term “plane splitting”refers to the process of taking a series of multi-bit pack data (such asa packed pixel) quantities and splitting off the bits of one or more bitposition within the series and repacking the split off bits intomulti-bit data quantities that only have the bits of one bit positionfor a the series of data quantities. Plane splitting is a way to take“pack pixel” arrays and convert them into “bit plane organized” arrays.Plane splitting may be done on the whole array or only on some subset ofthe array. Plane splitting is one of many ways in which incoming pixeldata may be reformatted (reorganized) for more efficient data processingor display manipulation.

For the purposes of the present invention, the term “pulse width” refersto the duration or length of a pulse. One example of how pulse widthsmay be controlled in accordance with one embodiment of the presentinvention is illustrated in FIG. 4. As can be seen in FIG. 4, the outputpulse width for each pixel value is different. For example, the outputpulse width for pixel value 2 is twice as great as the output pulsewidth for pixel value 1, the output pulse width for pixel value 3 isthree times as great as the output pulse width for pixel value 1, etc. Agiven “pulse width” is the duration in time between a single up and thendown transition or a single down and then up transition.

For the purposes of the present invention, the term “Read-Modify-Write”refers to a processes were a memory bit or bits are read, a computationis made based on those bit(s) and then written to the same location.While this is can support more general operations than a masked write,it generally takes longer. The masked write process used in a controlmethod of one embodiment of the present invention provides the samefunctionality without needing the extra steps of reading and modifyingfor a set of operations used in some embodiments of the presentinvention.

For the purposes of the present invention, the term “reallocation”refers to storing a new value in a given memory location based on nolonger needing that memory location for a previous value that was storedat that location.

For the purposes of the present invention, the term “row” refers to amemory organized row. A row of bits refers to all bits driven by asingle row driver.

For the purposes of the present invention, the term “scrollingsequential color” refers to illuminating a spatial light modulator withcolor bands of different colors, usually separated by dark bands, thatscroll across a spatial light modulator.

For the purposes of the present invention, the term “Set-Reset FlipFlop” refers to the well-known in the art storage bit circuit that has aseparate “Set” input that forces its output to a logical 1 and a “Reset”input that forces its output to a logical 0. If neither the Set norReset signal is active, then the output stays the same as it wasoriginally.

For the purposes of the present invention, the term “Single InstructionStream Multiple data Stream (SIMD) Processing” describes a class ofprocessing that has taken many forms. The basic concept is that thatthere is a single source of control instructions (Single InstructionStream) that issues a common memory addresses and execution operationsto multiple sets of data processing logic (Multiple data streams). Theadvantage of SIMD processing is that a single instruction controller andaddress generation logic can control many data operations. There are alarge number of variations on the basic concept.

For the purposes of the present invention, the term “single pulse”refers not only to a single pulse, but to two or more pulses that aresufficiently close together to behave substantially as a signal pulse.

For the purposes of the present invention, the term “spatial color”refers to a system wherein a color is given by a series of spatiallyseparate colors, generally including at least the 3 primary colors ofRed, Green, and Blue. An example of spatial color is the Red, Green, andBlue dots on a CRT television display. Spatial color may also be usedwith microdisplays by using small color filters over various displayelements.

For the purposes of the present invention, the term “spatial lightmodulator” refers to a one, two or multi-dimensional array of lightmodulating elements that control or modify incoming or emitted light.For example, a spatial light modulator may change the direction of theincoming or emitted light, the intensity of the incoming or emittedlight, the polarity of the incoming or emitted light, the wavelength ofthe incoming or emitted light, the focus of incoming or emitted light,etc.

For the purposes of the present invention, the term “subset” refers tothe conventional meaning of the term subset. For example, a subset of anarray of circuits may include all of the circuits of the array ofcircuits.

For the purposes of the present invention, the term “summary bit” refersto a combination of one or more bit positions for a given pixel. Forexample, two or more bit positions of a pixel may be OR'ed together toform a summary bit, two or more bit positions may be inverted and thenOR'ed together to form a summary bit, two or more bit positions may beAND'ed together to form a summary bit, two or more bit positions may beinverted and then AND'ed together to form a summary bit. A summary bitmay also be a unary single bit position or the inverse of a single bitposition.

For the purposes of the present invention, the term “time baseremapping” refers to using non-binary weighting of the timing control toweight the time of pulse width (s) based on incoming pixel values eitherinstead of or in conjunction with remapping the pixel values from aninput pixel value to an output pixel value such as is done with a “gammatable.”

For the purposes of the present invention, the term “time base” refersto how the backplane converts an ordered set of bits into the timeweighting of a pulse. Using a binary weighted time base where each bitposition of an ordered set of bits takes on a binary weighting is oneexample. The backplane that is the subject of the present invention insome embodiments may be flexibly programmed to handle non-binaryweighted time bases, or even have a time base that changes.

For the purposes of the present invention, the term “time base” refersto how an output pixel value translates into the time that an outputpixel is turned on or off. Also, that the time base is not necessarilylinear such that a linear change in the output value may have a linearor non-linear effect on the time a pixel is outputted. Furthermore, insome embodiments of the invention, more than one time base may be used.

For the purposes of the present invention, the term “variableallocation” refers to assigning use to parts of a single memory spacewhere the use of the memory space is not fixed to a particular purposeby hardware or software.

For the purposes of the present invention, the term “variable number”refers to a number that is not fixed.

For the purposes of the present invention, the term “vertical lines”refers to a vertical display line. In the descriptions below the termvertical lines or VL is to avoid confusion with the memory organization.However, there may or may not be a one for one correspondence with“lines” in a display and rows in one of the memories.

For the purposes of the present invention, the term “computer system”refers to any type of computer system that implements software includingan individual computer such as a personal computer, mainframe computer,mini-computer, etc. In addition computer system refers to any type ofnetwork of computers, such as a network of computers in a business, theInternet, personal data assistant (PDA), devices such as a cell phone, atelevision, a videogame console, a compressed audio or video player suchas an MP3 player, a DVD player, a microwave oven, etc.

For the purposes of the present invention, the term “deductive counting”and “deductive compares” refers to a control process were the control ofa pulse with can used less than all the bits of the value of the pulsedue to recursive feedback. The deductive “counting” or “compare” processmay not have a physical count/value that is being compared against, butrather the “count/value” a conceptual step in a process.

For the purposes of the present invention, the term “disable” refers toputting an output signal or data into a high impedance state. Generallythis is done so that one or more signals can share a common data set ofdata lines, often a bus structure. Generally only one set of signalswill be enabled while all other signals are disabled to the same dataline on a data bus.

For the purposes of the present invention, the term “drive bit” refersto a storage bit, often in a two-dimensional memory array, on which thedrive of an electrode is based.

For the purposes of the present invention, the term “ERAM” or “ExecutionRAM” or “execution memory” refers to an array of memory bits that are onthe spatial light modulator backplane that are at least in part used tocompute the output of the backplane. The bits may also be used for otherpurposes. The ERAM generally supports normal read and write operationsbut may be much wider than typical memory arrays to support SIMDprocessing including bit serial SIMD processing. It is anticipated thatin some embodiments, the so called MRAM and ERAM bits may be part of asingle memory array structure with a single set of addressing. In otherembodiments, the addressing of the MRAM and ERAM may be separate but thebits of each array may be interspersed in the physical layout of thetransistors. In other embodiments some or all the ERAM storage bits maybe physically separate from the MRAM bits.

For the purposes of the present invention, the term “floating node”refers to nodes that in the intended use can at some point be totallynot driven at all, such as with a bus with multiple drivers that can beput in a high impedance state or nodes where as some point the nodedriven to neither a high or low state. The circuitry associated with thelevel shifter with logic functionality (as described below in referenceto FIGS. 29, 30, and 31) has functionality where in if these “floatingnodes” are solidly driven to ground, the circuitry behaves one way, andif these nodes are allow to “float” they may be driven to up to anintermediate level (a level less than Vcc) by an N-Channel transistor.

For the purposes of the present invention, the term “implicit feedback”and implicit recursive feedback” refer to operations were the nextoutput value is dependent on the current output value but wherein thereis no physical wire or read operation required. An Set-Reset flip flop,for example, supports “implicit feedback” in that if neither the Set orReset input is active, then the output stays in it same state and thusis based on its previous state if neither Set or Reset is activated in agiven state.

For the purposes of the present invention, the term “MRAM” refers tomemory array that has in it storage bits that are “drive bits” (see thedefinition of “drive bits”) in it. In some cases the MRAM may have amixture of “drive bits” and storage bits that are not drive bits.

For the purposes of the present invention, the term “recursive feedback”refers to a process in which the next state of an output is based on afunction that includes the prior state of the output. The output may bea mirror copy of an output bit, may be inverted, etc. Also, there may beadditional drive circuitry and even some logical modification of thevalue between the output and the electrodes that drive the circuitry. Inrecursive feedback, results from one stage are fed back and combinedwith new inputs to compute the next value. In the descriptions of theembodiments below, this term is often used to mean feeding the outputstorage bit or a function of the output storage bit back to combine withnew inputs. This function may include a separate bit that is separatefrom the output storage bit that stores a function of the output storagebit. “Bit recursive feedback” is recursive feedback in which the outputof a given element is based on a single bit. For the purposes of thepresent invention, the term “recursive feedback” refers to any processin which a new output state is based, at least in part, on the oldoutput state. The feedback may be physical in terms of a wire or amemory read operation, or it may be “implicit” due to the way the datastorage structure and control operate. An example of implicit recursivefeedback is shown in FIG. 2.

For the purposes of the present invention, the term “visual displaydevice” or “visual display apparatus” includes any type of visualdisplay device or apparatus such as a CRT monitor, LCD screen, LEDs, aprojected display, a printer for printing out an image such as a pictureand/or text, etc. A visual display device may be a part of anotherdevice such as a computer monitor, television, projector, telephone,laptop computer, watch, microwave oven, electronic organ, automaticteller machine (ATM) etc.

DESCRIPTION

The present invention relates to a method and system for controlling aone or two-dimensional array of electrodes of a digital backplane. Inone embodiment of the present invention, the number of electrodes may bemany hundreds of thousands into the millions integrated on asemiconductor substrate. Due to the large number of electrodes in suchan embodiment, the cost of generating the control of each electrodebecomes significant and would generally discourage persons of ordinaryskill in the art from pursuing such a method or system.

In one embodiment of the present invention, the electrode may be amirror that both reflects light and creates an electric field thatcauses liquid crystal to modify the polarization of polarized light.Using a semiconductor CMOS substrate, such as silicon, GaAs, etc. tocontrol the Liquid Crystal in this way is known as Liquid Crystal onSilicon or LCoS. In other embodiments, this electric field may be usedto control a micro-mirror as in the case of a Texas Instrument's DLP™device.

In one embodiment of the present invention, the electrode may becontrolled in a digital on or off manner as compared to being controlledby an analog level. DLP™ stands for Digital Light Processing and as thename implies, the control of the light is “digital” and is controlled bya series of on or off pulses. It should be understood that other formsof display devices including those that emit light controlled by asemiconductor substrate may also use the techniques of the presentinvention. One such example would be Organic Light Emitting Diodes(OLED) devices where small LEDs would be controlled by the electrode.

Prior digital microdisplays takes some combination of the pixel valueand a Count to determine the new value of the electrode without regardsto the current state of the output storage bit. This type of processingis a “feed forward” function. However prior to the present invention noone has provided a way have the next state of the output be in some waydependent on the current state of the output.

In one embodiment of the present invention, recursive feedback is usedto significantly save memory on a digital backplane, the bandwidth tothe backplane and inside the backplane, and processing hardware whengenerating pulse width modulated signals on the display electrodes.

The general concept of digital LCoS devices has been known for well over10 years. U.S. Pat. No. 5,959,598 to McKnight, gives an example of manyof the basic digital LCoS concepts and the entire contents anddisclosure of this patent is hereby incorporated by reference. U.S. Pat.No. 6,650,138 to Zuravleff shows another variation of this“master-slave” mirror drive arrangement and the entire contents anddisclosure of this patent are hereby incorporated by reference. Both ofthe above patents describe using a feed forward drive method. Both showa two-storage-bit structure in which one of the storage bits is directlyshifted to the next bit for display and thus the two bits of storage areinexorably linked together and connected to a specific output.

It is one object of the present invention to use recursive feedback tolower the bandwidth compared to this method. Furthermore in oneembodiment of the present invention, rather than using a 2-bit shiftregister function, all the storage will be in RAM like bit arrays sothat no two bits of storage are directly linked together.

U.S. Patent Application Document No. 2003/0160803 to Willis), the entirecontents and disclosure of which is hereby incorporated by reference,shows a spatial light modulator microdisplay which uses a “feed forward”design. In this application, an N-bit pixel value is compared to a N-bitcounter and the result of that comparison is used to drive a displaymirror of an LCoS device. They show an N-bit wide comparison occurring2^(N) times in order to control the bit with each comparison requiringall N-bits. They show needing at least N-bits of memory storage on thedisplay device to affect the PWM control. This means that N-bits mustsomehow be sent/connect to an N-bit wide comparator 2^(N) times in orderto control the PWM waveform.

It will be a further object of the present invention to avoid requiringa multi-bit wide comparison to control an output. It will be a furtherobject of the present invention to use fewer than N-Bits on one or moreof the comparisons to reduce the need to fetch data. It will further bean object of the present invention to use significantly fewer than 2^(N)comparisons to determine a PWM waveform with 2^(N) different widths.

U.S. Pat. No. 6,326,980 to Worley, the entire contents and disclosure ofwhich is hereby incorporated by reference, shows another LCoS spatiallight modulator with a feed forward operation. In this case, theycreates a series of “equally weighted” and “binary weighted” pulses.Consistent with a feed forward drive, these pulses directly determinethe value on the light modulating electrode. Also, while the equallyweighted pulses are used to form a single pulse, the binary weightedpulses can cause one or more additional pulses. In other words, thismethod will not generate a single pulse for all N-bits if it isemployed.

It is a further object of the present invention to provide pulse drivemethod be capable of generating a single pulse or a constant number ofpulses. U.S. Pat. No. 6,326,980 does show in FIGS. 15 and 18 a processfor reading only some of the bits of an external frame buffer andlogically combining them, but then they are combined in what isdescribed as a parallel rather than bit, serial operation. However, thecombination is done outside the display device itself in an externalcontroller rather than in the display device itself. Due the processbeing a feed forward one, more bits have to be read and logicallycombined than would be required by the recursive feedback methods ofthis new invention.

PCT Patent Application No. WO0079510A1 to Guttag, the entire contentsand disclosure of which is hereby incorporated by reference, shows aspatial light modulator on a semiconductor substrate. PCT PatentApplication No. WO0079510A1 shows in FIG. 10 a display bit formed of 2latches where the data of the first latch may be shifted to the secondlatch. The application discusses reading from the memory array,operating on the bits and writing back to the memory. The only operationdescribed is for the inversion of the value in the memory for thepurpose of DC Balancing the LC material. While the bit one set may beinverted by this process, there is no description of how to control thewidth of the drive pulse on the bit. So while this operation involvesthe reading of the output state, this operation does not use other datato combine with the output bit. More specifically, PCT PatentApplication No. WO0079510A1 does not show how to control width of theoutput pulse by combining the current state of the output bit with otherdata.

It is an object of the present invention to provide a recursive processthat may generate a pulse width and not just invert a bit. It is afurther object of the present invention to show how to recursively usethe current display bit to generate a pulse width that uses the currentstate of the output bit without having to first physically read thestate of the output bit.

U.S. Application Document No. 2003/0103046 to Rogers describe anotherexample of a “feed forward” drive method and the entire contents anddisclosure of this application is hereby incorporated by reference.Similarly to U.S. Pat. No. 6,326,980, the present invention may use aset of equally weighted pulses for the most significant bits, butinstead of a series of binary weighted pulses as in U.S. Pat. No.6,326,980, it breaks the image into regions that feed a series of sharedcounters. It will be noted that the control from these counters is alsoa “feed forward” process and that the counts are done in parallel(multiple bits) and not bit serially as will be done in one embodimentof the present invention. A further object of the present invention willbe to generate a single pulse drive method that does not require thegeneration of “equal” or “fixed” time pulses. Another object of thepresent invention will be to significantly save processing hardware,memory storage, and memory bandwidth over prior digital backplanecontrol methods by using recursive feedback.

U.S. Application Document No. 2003/0103046, the entire contents anddisclosure of which is hereby incorporated by reference, also appears tobreak the display into large block regions that act with differenttiming which would to those skilled in the art be a potential source ofdisplay uniformity problems and other artifacts.

U.S. Application Document No. 2003/0210257 to Hudson, the entirecontents and disclosure of which is hereby incorporated by reference,shows yet another feed forward way to digitally drive an LCoS displaydevice. Even with the complexities of this scheme, it does not appear tosupport a single pulse width.

In one embodiment, the electrode may be controlled in a digital on oroff manner as compared being controlled by an analog voltage level. Inone embodiment, the electric field may be used to digitally control amicro-mirror, similar to the way that an electric field is used tocontrol a micro-mirror in Texas Instrument's DLP™ device. DLP™ standsfor Digital Light Processing and as the name implies, the control of thelight is “digital” and is controlled by a series of on or off pulses. Itshould be understood that the present invention may be used with otherforms of display devices including those that emit light controlled by asemiconductor substrate. For example, the present invention may be usedwith Organic Light Emitting Diodes (OLED) devices where small LEDs arecontrolled by the electrode.

Current digital microdisplays use some combination of the pixel valueand a count to determine the new value of the electrode without regardsto the current state of the output storage bit. This type of processingis a “feed forward” function. In contrast, the present invention employsrecursive feedback i.e. the current state of the output is used togenerate the next state of the output.

In one embodiment, recursive feedback is used to significantly savememory on a digital backplane, the bandwidth to the backplane and insidethe backplane, and processing hardware when generating pulse widthmodulated signals on display electrodes.

Furthermore in one embodiment of the present invention, rather thanusing a 2-bit shift register function, all the storage will be in RAMlike bit arrays so that no two bits of storage are directly linkedtogether.

The present invention provides the ability of controlling large arraysof electrodes in general and specifically of controlling large arrays ofdisplay elements that modulate light. The light modulation may be causedby changing the way the image elements transmit or reflect light or itmay be by controlling light emitting elements such as Light EmittingDiodes (LEDs) or the like. The methods for driving the electrodes andthe ways these concepts may be extended to driving large arrays ofelectrodes described below.

For digital microdisplay devices the output is generally held in a latchor storage bit. This control bit in turn is used to control the output.In the case of one embodiment of the present invention, the output is acharge on a mirror that controls Liquid Crystal material. It should beunderstood by one skilled in the art that there may be additional logicbetween the output storage bit and the mirror, in the case of LCoS, thisadditional logic may be used to invert the bit as part of a well-knownneed of LC material to be “DC balanced.” It should also be understoodthat the drive output bit take various forms, including a static RAMbit, a Dynamic RAM bit, or may have more than one bit in a master/slaveconfiguration as shown in U.S. Pat. No. 6,326,980 to Worley, the entirecontents and disclosure of which is hereby incorporated by reference.

In prior method of controlling outputs for microdisplay devices thevalue of the output is determined by some combination of the pixel valuewith counters and timing control. The result of this combination is useto generate the next output without regard to the current output.

In one embodiment of the present invention, a pixel value is combinedwith counters and/or timing control to generate one or more intermediatevalues. These intermediate value(s) in and of themselves are notsufficient to generate the next output value. This intermediate resultis then combined with the current drive output bit to create the nextoutput value.

As described below, the recursive feedback method of the presentinvention may be used to significantly reduce the data rate and/or theamount of logic and/or the amount of memory necessary to affect thecontrol of an array of outputs (in one embodiment of the presentinvention, on a display device). The fundamental reason for thesignificant savings is due to the current drive output bit havingaccumulated information in it that may be used instead of needing morebits from the original pixel value.

U.S. Patent Application Document No. 2003/0160803, the entire contentsand disclosure of which is hereby incorporated by reference, describesas single pulse method using a single count. Basically the pulse startedat time=0 and the pulse ended when the count reaches the pixel value.U.S. Pat. No. 6,326,980 to Worley, the entire contents and disclosure ofwhich is hereby incorporated by reference, describes breaking thecontrol of a pulse into a series of equally weighted pulses that areused to form a single output pulse representing the most significantbits using and a series of binary weighted pulses for the leastsignificant bits of the pulse value using a feed forward drive method.U.S. Patent Application Document No. 2003/0103046, the entire contentsand disclosure of which is hereby incorporated by reference, describesusing the equal pulse method of the Worley patent and then uses acounter or compare method control the LS bits in order to form a singlepulse.

A disadvantage of a single count with a feed forward compare method isthat it requires 2^(N) counts/compares of N-bits each or 2^(N) times N(N×2^(N)) total bits to be compared. The methods described in the Worleypatent and in U.S. Patent Application Document No. 2003/0103046 bothrequire equal pulse generation. It will be understood by those skilledin the art, that generating these equal pulses requires higher bandwidththan using encoded data and this why the equal pulse concept may not beused for the least significant bits as the bandwidth would be too high.If there are M-bits that have an “equal pulse” there are 2^(M) equallyweighted pulses that have to be generated.

It will also be noted that in the methods described in the Worley patentand in U.S. Patent Application Document No. 2003/0103046 that theequally weighted pulses of the MS-bits are shown preceding the controlof the LS-bits of the pulse(s) and in these methods the order of MSversus LS operation would probably have little if any advantage. Incontrast, embodiments of the present invention, described below mayprovide a cost advantage in processing the LS bits first.

FIG. 1 illustrates a prior feed forward control process 102. In step 104pixel data 212 and counters and/or timing control input 214 are used toproduce an intermediate value 116 by employing arithmetic and/or logicfunctions and/or storage. In step 122 an output control bit uses nextoutput value 116 to drive a mirror 132.

FIG. 2 illustrates a recursive feedback control process 202 inaccordance with one embodiment of the present invention. In step 204partial pixel data 212 and counters and/or timing control input 214 areused to produce one or more intermediate values 216 by employingarithmetic and/or logic functions and/or storage. In step 222 one ormore intermediate values 216 are combined with a current value 224 toproduce a next output value 226. In step 234 an output control bit usesnext output value 226 to drive a mirror 242 and current value 224 isgiven the value of next output value 226.

By comparing the processes in FIGS. 1 and 2, it is possible to seeimportant differences in the way a feed forward process (FIG. 1) and theway a recursive feedback process (FIG. 2) control an output.

With the recursive approach of the present invention, the current stateof an output is used to reduce the number of pixel value bits that willbe needed. For example, the table of FIG. 3 outlines a recursivefeedback method of one of the embodiments of the present invention. Thecounts from 0 to 7 are shown along with their binary representations 000to 111 with the right most bit value being bit 0 and the leftmost bitbeing bit 2.

FIG. 4 shows a simplified timing diagram for the control method shown inthe table of FIG. 3. Shown in the diagram of FIG. 4 are a pair ofwaveforms for the control and resulting output for each of the 8possible (0 to 7) pixel values. The pixel control is generated based ona given count shown on the X axis of the diagram. The logic thatgenerates the control is shared to generate the control for many pixelsand so the output value only has to be as long as necessary to affectthe control and this is indicated by the pulsing of the comparisons inthe control waveform. In a real world system there is also be some delaybetween the generation of the control information and the effect thecontrol information will have on the output and this is indicated by theslight delay between a control signal and the effect on the output.

The bottom pair of waveforms in FIG. 4 shows the control and output forthe control method assuming the pixel value is 0 (binary 000). Followingthrough the table of FIG. 3, at count zero since all 3 bits are 0, theoutput will not be turned on. On count 1 hardware will test for if bits2 and 1 are zero and since both are 0, hardware will generate a controlpulse that will cause the output to be driven off. But note that sincethe output is already zero, this additional setting of the output tozero has no effect on the output (the output remains zero). These“redundant” off pulses will happen for counts 2 through 7 as well. Theseredundant pulses are “don't cares” because these pulses have the sameeffect whether the pulses happen or not. The advantage of allowing“don't cares” pulses is that fewer bits have to be accessed to form thecontrol.

In FIG. 4, the next pair of waveforms above those for the pair for the 0value shows the control for the pixel value of 1 (binary 001). On count0, one of the bits, bit 0, will be a 1 so the table indicates to turn onthe output. So the output goes up/on after count 0. At count 1, bothbits 2 and 1 are 0 so a pulse is generated that will cause the output toturn off. It will also be seen that on count 2, which looks at bits 2and 0, since bit 0 is a one, the test will fail and no pulse will begenerated. The output will stay in its current state. Then on count 3,on bit 2 is tested and since for the binary pixel value 001, it is zero,a pulse is generated. But since the only effect of this pulse would beto turn off an output that is already off, it has no net effect.Following through the table FIG. 3, at count 5, which reads only bit 1,which is zero for a pixel value of 1 (binary 001), another redundantpulse is generated which has no effect on the output.

Referring to the table of FIG. 3, it may be observed that bit 2 is notlooked/used in counts 4 to 7. Thus if storage is at a premium, it is nolonger necessary to keep this bit available after the comparison forcount 3 is made or about ½ the time. Similarly bit 1 is last looked atin the caparison for Count 5 and is not used in counts 6 and 7, and bit0 is last looked at in count 6. In one embodiment of the presentinvention, memory used to store bits is continually reallocated tominimize the total storage requirement.

Looking at the rest of the timing diagram of FIG. 4, it will be seenthat there are redundant pulses generated only after the output isalready zero. An advantage of allowing these redundant pulses is thatfewer pixel input bits are required to decide on the generation of at agiven time and it this in turn will result in the need for less storageon the display device.

The previous discussion has describe a method of the present inventionin terms of a series of “counts”, but in practice there may never aphysical comparison to a counter as done for Example in PatentApplication Document No. 2003/0160803 (application Ser. No. 10/086,010),the entire contents and disclosure of which is hereby incorporated byreference. Various bits are looked at a given point in time, but theyare not compared to a counter but which bits are looked at are based ona sequence of operations. In more advanced embodiments of the invention,the “count” becomes more of an abstraction rather than a physical value.

For the cases for the table in FIG. 3, the bits that are looked at agiven count, correspond to the zeroes in the count. For example forcount 2 (binary 010), bits 2 and 0 are looked at. Since it steps throughall the counts from 0 to 7, over the 8 counts, the number of 0's will beexactly half the total number of bits. Also, while the method of thepresent invention is used to control a pulse of any width, the onlylogical operation needed is a logical OR or a logical NAND (Inversion ofan logical AND which is equivalent to a Inversions of all inputsfollowed by a logical OR). There is no need for a arithmetic comparisonas in Patent Application 2003/0160803, nor even an equal compare thatwould require a series of XORs of each bit to a count followed by an OR.This simplicity of the operations required to perform this test will beadvantageous due to the very large number of pulses that will becontrolled for a high resolution display.

It will be obvious to those skilled in the art that the processdescribed may be extended to any number of bits of pixel size values andcorresponding series of pulse widths. On average, only half the bitsneed to be looked at for any given count, so that, for example, an 8-bitpixel value size, on average only 4 bits will be looked at to determinethe intermediate value as is shown in FIG. 2. This intermediate valuewill then be combined with the current value to control the pulse width

Looking at the table in FIG. 3, it will be seen that the process skipsaround from bit location to bit location. For example on count 0 itneeds all 3 bits. On count 1 it needs bits 2 and 1. On count 2 it needsbits 2 and 0. In one embodiment of the present invention, the bits arebe stored in a large array of bits and fetching bits that are not neededwill end up wasting bandwidth which in turn would mean higher clockrates.

To avoid wasting bandwidth, a technique known as bit serial processingmay be employed. Bit serial processing stores each bit of precision at adifferent memory address. To control the massive number of outputs usingbit serial processing a technique known as Single Instruction, MultipleData Stream (SIMD) processing maybe employed one embodiment of thepresent invention.

In some embodiments of the present invention, a recursive feedbackprocess is used in which an array of outputs that are stored, the“current outputs” are used in determining the next state of the outputs,the “next outputs.” In some embodiments of the present invention, a verylarge number of outputs are controlled so it is important in such anembodiment to have an efficient means of storage while supporting therecursive feedback.

There are many possible ways to implement recursive digital feedback inaccordance with an embodiment of the present invention. FIG. 5illustrates a circuit 502 using explicit recursive feedback in which aClocked “D” (delay) flip flop 512 output 513 feeds back through amultiplexer 514. An enable bit 516 controls multiplexer 514 to choosebetween a new input value 522 or an old output from D-flip flop 512,indicated by data line 524, to D-flip flop 512. Enable bit 516 may be,for example, an “intermediate value” shown in FIG. 2. Multiplexer 514selects the old output if enable bit 516 is 0 and new input value 522 ifenable bit 516 is 1. Connection 532 indicates an output 532 ofmultiplexer 514 that become an input of D-flip-Flop 512. A clock pulse542 causes the input of D-flip flop 512 to become a new output 513 ofFlip-Flop 512 as is well known in the art. A feedback signal, indicatedby data line 524, of new output 105 is input back in to multiplexer 514as an old D-flip flop output 513. Feedback signal 524 corresponds toexplicit feedback for the circuit 502.

The D-flip flop and the multiplexer used in the embodiment of FIG. 5 maybe any suitable D-flip flop or multiplexer. In one embodiment, the newvalue of FIG. 5 may be one control signal, such as one of the controlsignals shown in FIG. 2. Also the enable bit in FIG. 5 may be the resultof some logical and arithmetic operation on some part of the pixel dataand timing and control signals shown such as the “intermediate value(s)”shown in FIG. 2 and described above. For a spatial light modulator therewill be an array of outputs. Thus, some embodiments of the presentinvention will support processing many bits of output. In particular, insome embodiments a large number of output bits may be processed inparallel.

It will be understood by those skilled in the art, that the clock signalof FIG. 5 does not need to be a continuous clock, but may be a clockthat is enabled or gated. FIG. 6 illustrates a circuit 602 employingimplicit feedback that is functionally equivalent to the circuit of FIG.5 for most purposes, but that is implemented differently. A clock pulse612 and enable bit 614 go to an AND gate 614 to generate a clock input,indicated by connection 622, to a D-flip flop 624. The arrangement ofcircuit 602 has the effect of preventing D-flip flop 624 from changingif enable bit 614 is zero. Thus output 626 of D-flip flop will either bea new value 632 if enable bit 614 is a 1 or will stay the old value ifenable bit 614 is a zero. Another way of viewing the circuit 602 is thatclock 612 is as an unconditional write enable to the D-flip flop 624 andbit Enable 614 acts as a “bit mask” to enable or mask off the writing.

Thus the logic of FIG. 6 performs the same function as the logic of FIG.5. In the logic of FIG. 5, the recursive feedback is explicit with theoutput feeding back as a feedback signal to the multiplexer logic. Incontrast, in the logic illustrated in FIG. 6 the feedback is implicit.While the implicit feedback is less general, it may be significantlymore cost effective for many applications.

In prior circuits that employ feed forward methods, the maindetermination is what to write (a one or zero), whereas with implicitrecursive feedback method, such as employed in embodiments of thepresent invention, a determination is made whether to write with thedata/value that is written being pre-determined before any comparison orother computation.

While the concepts of the present invention may be implemented withClock D-flip flops, others forms of storage are often much more costeffective for the large amounts of storage that may be required for aspatial light modulator, currently many thousands to millions ofoutputs. Thus in one embodiment of the present invention, a more costeffective method using an arrayed structure of Static RAM (SRAM) bits isemployed. However, it will be understood that types of memory other thanStatic RAM may be used to implement embodiments of the presentinvention. Also, although a SRAM has a variety of capabilities, someembodiments of the present invention takes advantage of a relativelylittle used capability of SRAM, namely to use “masked write” drivecircuitry external to the array of bits that makes the each of bitsbehave like Set-Reset flip flops or the Circuit of FIG. 6.

FIG. 7 shows a mirror bit cell 702 which has a common 6 Transistor (6-T)SRAM bit 703 connected to a mirror 704 controlled by electrodes (notshown). SRAM bit 703 may also be referred to as a drive output bit sinceSRAM bit 703 is connected to circuitry that drives a mirror. SRAM bit703 uses cross-coupled inverters 712 and 714 to store the bit value. Thewrite process of SRAM bit generally begins with bit lines 714 and 716both precharged. To write a value into SRAM bit 703, one of either bitline 716 (-bit) or 718 (bit) is first pulled down by drive circuits (notshown) outside the array of SRAM bits (not shown). Then a row select 726is turned on, allowing bit lines 716 and 718 to drive into SRAM bit 703through transfer gates 728 and 730 and thus writing to SRAM bit 703.Mirror bit cell 702 may optionally include a DC balancing block 742indicated by ghost lines.

In an SRAM bit such as the SRAM bit shown in FIG. 7, on read operations,both bit lines are typically precharged before attempting to read orwrite to the bit. The electrical design of the SRAM bit, includinginverters and transfer gates, is such that the SRAM bit will not changestate if both bit lines are precharged, and whichever inverter in theSRAM bit is outputting a zero will pull down the bit line connected tothat inverter through the transfer gates. Generally, circuitry externalto the array will sense which bit line is being pulled down or thedifferent in the bit lines when doing a “read” operation.

Also, there may be other logic or transistors in an implementationbetween the drive output bit and a mirror or the electrodes that controla mirror. For example, there may be logic that selectively inverts thevalue that drives the mirror to support the DC balancing requirement ofLC material, as indicated by the DC balancing block in FIG. 7.

FIG. 8 shows a logical representation of a simplified 2 row by 2 columnSRAM 802 including drive circuitry that is generally external to thearray of bits. Four SRAM bits 804 are shown organized in 2 rows and 2columns. Precharge transistors 812 pull up all the bit lines (-Bit) 814and bit lines (Bit) 816. On write operations, the data on the commondata-in/data-out line 820 is sent to a three state buffer (One, Zero, orfloat) 824 and to three state buffer 826 through an inverter 828 of aread/write circuit 830 indicated by a dashed rectangle. A single writeenable (WE) signal 832 turns on three-state buffers 826 and 824 of allthe selected columns (column decoding is not shown in this simpleexample) causing the binary value on data line 820 to be driven on bitlines 814 and 816 due to inverter 828. On write operations, the readsignal of off has the effect of disabling/tri-stating read output buffer834. A single row select line (n) such as 836 or 838 in this simpleexample will be turned on via row Decoding and drive Circuitry (notshown) and one of the bit lines 814 or 816 for each bits connected tothat row select line will be driven low by drives 826 or 824 for eachcolumn which in turn will cause the selected bits to be written based onthe bit lines. During write operations, read output buffer 834 istri-stated (floated) so that data may be driven in on data line 820.

On read operations, the bits are precharged via the prechargetransistors 812, the write enable is off thus tri-stating the writebuffers 826 and 824, and one row select is on. All bits on a row willpull down one of the two bit lines for each column based on the state ofa bit that is selected by the row select for that column. The “senseamplifier” 844 detects which of the two bit lines in each column isbeing driven lower by the row selected bit in that column and the outputof sense amp 844 is connected to the input of the data out buffer 834which on read operations with read Enable (RE) 846 turned on, will driveout on the common data-in/data-out line 820. Commonly, one of the senseamplifiers may amplify the difference between the corresponding bit and-bit and will output a strong binary level. The three level buffers willthen be enabled by the read enable to drive the data out on the datalines.

FIG. 8 is a simplified example both in terms of the number of bits andthe circuitry shown. For example, only the SRAM bit is shown, but otherdevices or circuits such as a logic, an electrode, a mirror, etc. may beconnected to the storage bit as shown in FIG. 7. Also it will beunderstood by those skilled in the art that there are many ways toimplement a RAM array and the associated buffering. Also a “columndecoder” is well known to those skilled in the art is not shown forsimplicity and may be used in a RAM array.

FIG. 9 shows a small 2 row by 2 column array 902 that demonstrates asimplified write mask SRAM design that supports a masked write of anembodiment of the present invention. Four SRAM bits 904 are shownorganized in 2 rows and 2 columns. A masked write driver 906 is shown bya dashed rectangle. Precharge transistors 912 pull up all the bit lines(-Bit) 914 and bit lines (Bit) 916 for all the column that may bewritten. A data line 922 and its logical inverse -Data line 924broadcasts a value to some or all of the columns of array 902. Takentogether, Data 922 and -Data 924 resent a single M-Data value 926. Array902 also includes a single write enable (WE) signal 932, a row selectline (n) 936, a row select line (n+1) 938, a per bit write enable 942,and a preset signal 943 (Pre).

In masked write SRAM 902, what would be the data in for a normal SRAMbecomes a series of bit write enables 942 when taken together form a“bit mask” that enables a write operation on a bit by bit basis. Writeenable 932 is still broadcast to control the timing of the possiblewrite, but unless per bit write enable 942 is also on, then the M-data926 represented on Data line 922 and -Data line 924 will not be able topull down either bit line 914 nor 916 through transistors 944 and 948 inthe case of bit lie 914 nor transistors 926 and 950 in the case of bitline 916. If per bit write enable 942 is off, then transistors 944 and954 will both be off so that even though write enable 932 is on thusturning on transistors 948 and 948 the neither of bit lines 914 and 916will pull down. Since neither bit 914 or 916 line pulls down, a givenSRAM bit 904 “sees” what looks like a read cycle. This is referred to asa “dummy read” since bits lines 914 and 916 may be driven as in a readcycle of FIG. 8, but there is no output.

Bit WE, write enable 942, for each column turns an “unconditional” writeof each column into a “conditional” write per column. Also the “true”data signal 922 may be viewed as a “Set” signal and the “false”-datasignal 924 may be viewed as a “Reset” signal that is enabled by bit WE(or enable bit) 942. The circuitry of FIG. 8 may also be viewed asextending the concepts of FIG. 6 for a single bit, in an efficientmanner for controlling an array of bits.

As shown FIG. 9, while the output in the flow diagram of FIG. 9 showsthe output bit going out of the output bit, into a “combine” block, andback into the output bit, some bit storage array structures, such asmany RAM structures can support this “combining operation” withoutneeding explicit combining hardware by what is known as a “masked write”operation. Additional functions such as those for DC Balancing are notshown in FIG. 9 but may be employed in embodiments of the presentinvention.

It will be understood by those skilled in the art that there are manydifferent ways to buffer and drive the data signals of the Data line and-Data line. For example a single data signal may be driven with and theinversion would be generated locally within each drive bit. Forgenerality and simplicity in other figures only a single M-Data Line isshown, but it should be understood that many embodiments may beimplemented with a pair of lines as shown in FIG. 9.

Logic and operation of bit lines in FIG. 9 are the same as for a normalSRAM, such as the more normal SRAM shown in FIG. 8. One differencebetween the write mask SRAM of FIG. 9 and a normal SRAM of FIG. 8 is thedifference is how the bit lines are driven. In FIG. 8, only the logicfor the SRAM bits is shown, but other logic, electrodes and mirrors maybe added to bit to form a display element.

It will be noted that there is no sense amp or other mechanism to readshown in FIG. 9. For the functional operation of one embodiment of thepresent invention, that of driving an electrode that controls a displayelement, there is no need to physically read the bit. The recursivefeedback, comes from the way the masked write operation is performed andis in this case “implicit feedback,” as was discussed with respect toFIG. 5 and FIG. 6 above. It will be understood by those skilled in theart, that logic may be added to support a read operation if it isrequired, for example, for testing reasons or for added functionality.It will also be understood by those skilled in the art that while acolumn decoder is not shown, but may be added.

Also, the logic shown in FIG. 9 is only one of many ways to implement amasked write driver and is only one example. It will also be understoodby those skilled in the art that a per bit or multiple bit “maskedwrite” function may be supported by RAMs using other than the 6-T RAMbit of this example. An important difference with respect to a normalRAM is that a single data value is broadcast to at least some of thecolumns, and whether a write is performed is controlled on those columnsa column by column basis, whereas in a normal RAM the write enable isbroadcast and the data varies by column.

The logic shown in FIG. 9 is only one of many ways to perform a maskedwrite. The effect of a masked write may be performed in many differentways as is known to those skilled in the art. An important part of amasked write is to be able to inhibit the writing to memory based onwhat is in effect data, the per bit write enables. FIG. 9 shows how bychanging only the column drive circuitry, that the same storage element,a RAM bit, may be used. It will be understood by those skilled in theart, that the exact design of the storage element may be different thanthat of the 6-T SRAM illustrated and/or the drive circuitry shown inFIG. 9.

While a masked write is not required for the recursive feedback conceptof the present invention, a masked write has the advantage of notrequiring the extra step of reading the output bit in order to beeffectively combined with other data. In other embodiments, the bit maybe read first to explicitly perform the recursive feedback.

It will be understood that the SRAM array shown in FIG. 9 is only asimple example for illustrative purposes only. The actually array for adisplay may have 1000 or more rows and 1000 or more columns of bits. Itshould also be understood that RAM types other than those using SRAMbits may be used.

A major advantage of a masked write type RAM is that a masked write typeRAM may economically support some forms of recursive feedback typemethods without requiring the storage bit to be first read. Also, thestorage bit itself need be no different than that of typical RAM andsince for a large RAM array, the size of the bits themselves dominatesthe area, a masked write RAM may be built in about the same area as aconventional SRAM. Similarly masked write type drive methods may besupported on RAMs with memory bits other than SRAM bits.

While not all recursive feedback algorithms may use the write mask typeSRAM shown in FIG. 9, some embodiments may use methods that can takeadvantage of it. In particular the recursive feedback and deductivecompare methods shown in FIGS. 3 and 4 can take advantage of the maskedRAM. The masked write bit Enables of FIG. 9 may be driven by the controlsignals shown in FIG. 4, where there are a set of control signals for aseries of drive bits that are going to be conditionally modified in asingle operation to a RAM supporting masked writes.

An example of one way to implement a feed forward method for an array ofdrive output is described in Application Document No. 2003/0160803, theentire contents and disclosure of which is hereby incorporated byreference. Assuming one again the very simple 3 bit controlled pulse ofFIG. 3 using the methods taught by U.S. Patent Application Document No.2003/0160803 to Willis, the pulse width would be formed by comparing the3-bit pixel value to a 3-bit counter. For each count, all 3 bits of thepixel value are compared to all 3 bits of a counter. If the count is,for example, greater than the pixel value, then the output (mirror) isturned off. If we assume that the 3 bits of pixel value are stored in amemory or register file some place, then if the 3-bits are read for eachof the 8 counts, a total of 3×8=24 bits must be read and 8 unconditionalwrites are performed per pulse per drive bit. But using the DeductiveCompare method of FIG. 3 combined with a masked write memory taught bysome embodiments of the present invention, only 3×4=12 bits need to beread per drive output to control them.

In some embodiments of the present invention, a “dual count” method isemployed where the pixel value will be processed in terms of MS-bits andLS-bit but where there is no need to generate “equally weighted pulses”as are required in prior art references mentioned earlier (U.S. Pat. No.6,326,980 and U.S. Application Document No. 2003/0103046). In oneembodiment of the present invention, both the MS and LS control will bepart of a single process without needing separate and distinct hardwarefor MS and LS control. Furthermore in one embodiment of the presentinvention the split of what are considered within a pixel value to be MSand LS bits may be changed without significantly altering the hardware.

A basic concept of the dual count method of one embodiment of thepresent invention is to break the single count for a single N-bitcount/compares as in reference '803, into two counts/compares of lessthan N-bits. Each of these sets of counts will form an LS Part and an MSPart of the whole count. The LS part will be associated with some set ofleast significant bits and the MS Part will have the remaining bits. Thefirst stage, in some embodiments the LS Part will act as a “delay untilstart.” The second stage, in some embodiments the MS Part, will be a“continue until” value. As is well known, an N-bit number can have 2^(N)values. By splitting a single N-bit Count into a “count” of A-bits and(N−A)-bits, the total number of “counts” to perform is then 2^(A) plus2^(N-A). For any values of A and N were A<N, (2^(A)+2^(N-A))<2N.Furthermore it should be understood that there are only A bits tocompare for each of 2^(A) steps plus A-N bits to compare for each of2^(N-A) stages. By controlling the start of a pulse with A-bits andcontrolling the end of a pulse with N-A bits, the pulse can have 2^(N)different widths, but there are less count stages required and therewill be many less bits that need to be compared against.

So where for a single count method such as the method described in U.S.Patent Application Document No. 2003/0160803 there are N×2^(N) bits tobe compared, the method of the dual count method of the presentinvention requires A×2^(A)+(N−A)×2^(N-A). So for example if N=8 and A=5then for a single count method there are 8×2⁸=2048 bits to be compared,there are 3×2³+5×2⁵=184 bits to be compared in the dual count method ofthe present invention, which is a significant drop (about 11 times) inthe bit comparisons that have to be done.

Furthermore, in one embodiment of the present invention, the deductivepulse width control described with respect to FIG. 3 above may becombined with this dual pulse control method to cut the number of bitcompares that have to be done in half again so that only 92 bitcomparisons have to be done (or about 22× less than a single pulsemethod) to control a pulse with N=8 and A=3. Dropping the number of bitcomparisons required will greatly lower the some combination of theprocessing speed and processing hardware required. A minima in thenumber of operations occurs when A is ½ of N (if N is even or thenearest integer up or down if N is odd) so that if N=8 and A=4, thenumber of bit compares required would be ½(4×2⁴+4×2⁴)=64 bit compares.

Another advantage of the dual compare algorithm used in the presentinvention is that the algorithm can free up memory used to store theleast significant bits, this may be particularly important if thestorage is on the display device. The LS-Stage is counting at nominallythe LS-counting rate. If the LS-stage is done first, the need for thesebits may be completed rather quickly and the memory required for themmay be used for other data. Consider the example of the 4/4 split of an8-bit pulse width. If the entire pulse width time is “W” then theLS-Bits will be completed in about W/16. Thus for 15/16th of the time(assuming simple binary pulse weighting) the bits are not needed.

As described in FIG. 3 above, the MS and LS bits may also be freed upover time using the deductive counting method since at some time thoughthe algorithm, some bits are never looked at again. The combination ofDual Compare and Deductive compare algorithms may allow the digital beused to significantly reduce the on-display storage requirement.

A dual counting with deduction process in accordance with an embodimentof the present invention is shown in FIG. 10, which illustrates a 4/4split example. Time is shown starting at the LS-bits and continuingthrough the MS count. The diagram shows the MS-Counting intervals withthe LS-Counting intervals expanded below it for clarity. Shown on thediagram are the times when the bits are freed up and are no longerneeded for the pulse generation process. Shown below the timing diagramof FIG. 10 is an example of how the pulse expands with increasing pixelvalues.

The control of the electrodes in one embodiment of the present inventionmay use memory for the control of the output bits plus some amount ofmemory for the storage of all or partial pixel values used to controlthe mirrors. The amount of storage required may vary with the displayrequirements and the bandwidth available. One of the advantages of thepresent invention is the relative ease with which these trade-offs maybe made.

While it is possible to use the concepts of the present invention with asingle homogeneous memory for the on-display, it may be advantageous tobreak the memory into regions, and even use different types of memoryfor those bits that more directly drive the output electrodes from thosethat are used for computing the pulse widths.

In one embodiment of the invention, mirror RAM is used to drive outputelectrodes that drive mirrors. Because of the close connection betweenthe output electrodes and the mirrors these electrodes drive, thecombination of an electrode and the mirror the electrode drives issometimes referred to in the present invention by the term“electrode/mirror”. It should also be understood, that phrases such as“controlling a mirror” may also refer to “controlling an electrode thatdrives a mirror.” For the purposes of this description, memory that moredirectly drives a mirror will be referred to as mirror RAM or MRAM andbits within this memory array will be called MRAM bits Also, that theremay be other logic between the storage bit itself the electrode/mirror.It should also be noted that while a 6-T Static RAM is used in oneembodiment of the present invention, that any other type of bit storagemay be used, including bits that would not be considered to be “StaticRAM bits.”

For the purposes of this description, memory on a display device that isused as data in computing the pulse width on a per output basis will bereferred to as the Execution RAM or ERAM. It should be understood thatthe ERAM may in some embodiments be a physically separate memory or maybe a part of some other memory including a single memory containing bitsused as ERAM.

While the MRAM and ERAM memories are discussed as being logicallyseparate memories, they may be physically interposed in an integratedcircuit layout. In one embodiment of the present invention, there is anMRAM bit under every mirror. There may be from no ERAM bit to many ERAMbits under a mirror. It should be understood that in some embodiments,that MRAM and ERAM bits may even be part of a single memory array withcommon ROW and/or column circuitry.

FIG. 11A illustrates in simplified form a memory array circuit 1102 witha mix of MRAM and ERAM bits of the present invention. FIG. 11Billustrates in expanded form a set of components 1106 of memory arraycircuit 1102 for a single mirror/electrode 1106 shown as a dashed box.In an LCoS device of one embodiment, the mirror will cover much or allof the circuitry shown in FIG. 11B. Each set of components 1106 includesone MRAM bit which includes an RAM bit such as that shown in FIG. 7 andfour ERAM bits 1118 (that may be ordinary memory bits) that are arrangedunder a single display mirror/electrode 1106. MRAM bit enable/mask input1122 provides bit enables to control the masked RAM drivers 1123 todrive bit line(s) 1124 of the MRAM bits 1112 on a column by column basisas explained in FIG. 9. The ERAM data input and output 1125 providespath for data from ERAM bits 1118 to be read or written via bit line(s)1144 through the column decoder 1126 and sense amp/column drives 1148such as are commonly found in an ordinary memory shown in FIG. 8.However, the memory of FIG. 8 does not include a column decoder.

It will be understood by those skilled in the art, that while single bitlines are shown going to MRAM and ERAM bits, they may in fact be, forexample, a complementary pair of bit lines as is common in some types ofmemory arrays.

The MRAM bit may have other logic between its storage bit and aconnection 1127 to mirror/electrode 1106, as shown for the MRAM bit inFIG. 7. While the ERAM bits may be simple storage bits they may alsohave additional circuitry associated with them in other embodiments.

The 6 MRAM bits 1112 shown in FIG. 11A taken together form a 3 column bytwo row MRAM array. Each ROW has a separate MRAM row select line 1128.The 24 ERAM bits 1118 shown in FIG. 11A form a 6 column by 4 ROW ERAMmemory array. In the example of FIG. 11A, there are separate MRAM andERAM memories that are physically interposed, but they may operateindependently. Row select lines 1132 are used, in this simple example,to select a ROW of 6 MRAM bits 1118. For the MRAM array there are 3column bit lines 1124, one for each of the columns of MRAM bits in FIG.11A. In this example, the MRAM does not have a column decoder, but onemay be used in other embodiments. There are six ERAM column bit lines1144, one for each of the six columns of memory bits shown in FIG. 11A.Each pair of column bit lines 1144 is shown going to a 2 to 1 columnDecoder 1126 as is well known in the memory art. Column decoder 1126selects one of the pair of bit lines connect to it to be active on reador write cycles. Sense amps and drivers 1148 senses the bit linesthrough column decoder 1126 on reads and drives the bit lines throughthe column decoder 1126 on writes. The ERAM data input and output 1125goes to the sense amps and driver circuitry 1125. Not shown in FIG. 11A,but well understood in the art, there will be read and write selectlines (or their equivalents) for controlling the sense amps and drivers1148 to control the read and write process to the ERAM bits.

In the embodiment of the present invention illustrated in FIGS. 11A and11B, the column driver logic for MRAM bits 1112 have masked writefunctionality with mask drivers 1123 similar to the mask driversdiscussed above. ERAM column drivers do not necessarily support maskedwrite functionality and have set of sense amps and drivers 1148 of aconventional memory. One of the many ERAM row select lines 1132 aredriven by ERAM row decoder and drivers 1172 which are addressed by anERAM row address 1174. Column decoder 1126 uses a column address 1180 toselect between the pair of bit lines shown in FIG. 11A. MRAM bits 1112support mask write driver 1123 by supporting mask write driver logicwith a common write Enable 1188 and bit enable line, bit line 1124, thatacts as a per bit masked write enable, input 1122. An MRAM row decoderand drivers 1190 that are address by MRAM row address 1192 drive one ofmany MRAM row select lines 1128 to enable the masked write function to agiven MRAM bit in a column.

It will be understood by those skilled in the art that FIG. 11A and FIG.11B show only a simple example. The number of rows and columns and thevarious decoders may be varied as is well understood by those skilled inthe art. This example shows the MRAM and ERAM bits physicallyinterposed, but still kept as logically separate memories, but it willbe understood by those skilled in the art that in some embodiments, theymay be combined into a single logical memory array or separated intomore than two logical memories. It should also be understood that theuse of the masked write type memory for MRAM is only one potentialembodiment of the invention. Also, in the embodiment illustrated inFIGS. 11A and 11B, there is only figuratively one “bit line” shown percolumn of memory bits, but this may be two lines of a differential pairas is common in some RAM designs. In the embodiment of FIGS. 11A and 11Bthe ERAM sense amps and drivers are assumed to be that of a conventionalmemory and the write and read enables are not shown.

It will be understood by one skilled in the art that there need not bean integer number of ERAM bits per mirror, there may, for example, beone or more bits that straddle the gap between two or more mirrors. Inaddition to the MRAM and ERAM there may be other memories used forgenerating broadcasted values shared by multiple pulses and forcontrolling the operation of the device.

A SIMD processor generally contains three major blocks, the controller,memory and/or registers, and processing elements. The memory holds allthe data and results from the processing. The processing elements or PEsis the name commonly given to the multiple data paths. In its simplestform, all the PEs do the same operations but on different data asprovided by the memory associated with each PE. The controller generatesall the memory addressing, control sequencing, and sends controls to theprocessing elements.

SIMD processors have been defined both with bit-parallel and bit-serialdata paths within the PEs. The digital backplane of the presentinvention may make use of either a Bit-Parallel SIMD or Bit-Serial SIMDor even a combination thereof. But, a bit serial SIMD has someparticular advantages for use in a digital backplane in accordance withone embodiment of the present invention.

U.S. Pat. No. 5,990,982, the entire contents and disclosure of which ishereby incorporated by reference, shows the use of a SIMD processor todo processing external to a Microdisplay, namely a Texas InstrumentsDMD™ display. While SIMD processing has been used previously in displaysystems external to the display device such as described in U.S. Pat.Nos. 5,990,982 and 6,493,467, the entire contents and disclosures ofwhich is hereby incorporated by reference, SIMD processing is not usedinside the microdisplay itself.

The term “Smart memory” generally refers to a device that has a largeamount of memory and some processing or other special features connectedto it. The processing is often some form of SIMD machine such as in U.S.Pat. No. 5,184,325, the entire contents and disclosure of which ishereby incorporated by reference. U.S. Pat. No. 4,720,819 shows a fastway of clearing a memory a row at a time and U.S. Pat. No. 4,959,811shows how to put a Bit-Parallel comparator on the edge of a memory, andthe entire contents and disclosures of both these patents is herebyincorporated by reference.

FIG. 12 shows a 1-bit wide “slice” 1202 of MRAM and ERAM input andoutput buffers 1204 and a PE (processing element) 1206 that supports oneembodiment of the present invention. bit lines 1208 indicated by atwo-way arrow connect a memory array (not shown) of mixed MRAM and ERAMsuch as is shown in FIGS. 11A and 11B to input and output buffers 1204Global control signals 1210, 1211 and 1212, 1213 and 1214, labeled as agroup 1216 are sent in one embodiment to a linear array of PEs, of whichPE 1206 is an example, to control operation of each PE. In thisembodiment all PEs along one edge of a given memory array (not shown)will receive the same global signals but it should be understood that inother embodiments, there may be multiple sets of global signals withdifferent controls to various groups of PEs.

There are no cross communication signals shown in this embodimentbetween two or more PEs, but is well known in the SIMD processing artthat cross communication between neighboring PEs can sometimes beuseful. It is anticipated than in other embodiments there may be signalscommunicating data or other information between PEs.

ERAM of the memory array (not shown) of this embodiment acts as aconventional RAM and is addressed with row and column addresses.Compared to most common RAMs, however, the ERAM has a relatively wideoutput, in this embodiment, one bit per PE. The number of PEs may bemore or less than the given number of MRAM outputs associated with aLine of the display running in the same direction as the columns of theMRAM and ERAM, but in this one embodiment, it will be assumed that thenumber of PEs is the same as the number of MRAM columns and that thereis one MRAM column per Line of outputs. In other embodiments, there maybe more or less PEs than there are MRAM outputs.

ERAM data line 1218 is 1-bit of output from the ERAM. Control signal1210, which acts as the Global PE Function control signal, selects theoperation from logic block 1220 shown as a dashed box. If control signal1210 is a zero, then the output of AND gate 1222 is a zero regardless ofthe state of an output 1224 of a logic block D-flip flop 1226 and thusthe data on data line 1218 is OR'ed with zero by OR gate 1228 and thusthe output of XOR gate 1232 passes unmodified to the input of logicblock D-flip-Flop 1226. If control signal 1210 is a 1, then the outputof AND gate 1222 is the same as output 1224 and thus OR gate 1228 willoutput the OR of the output of XOR gate 1232 and output 1224 to theinput of logic block D-flip-Flop 1226. The control signal 1212 is use toselect when to look at the output of OR gate 1228 and save the result.The storage D-flip flop and feedback path through AND gate 1222 and ORgate 1228 when control signal 1210 is a logical 1, will logically ORtogether the output of XOR gate 1232 each time the clock input signal1212 is applied. The more bits that are to be OR'ed together the morecycles it takes, but the width of the OR may be variable. Performing amulti-bit-wide OR over multiple cycles is a form of bit serialprocessing.

Control signal 1214 is used to control whether the ERAM data output 1218is inverted or not by XOR gate 1232. If the signal 1214 is a 1, then thedata on output 1218 is inverted before going to OR gate 1228. Thus thelogic block 1220 in conjunction with D flip flop 1226 can OR together aseries of bits or their inverses coming over data lines 1218. In someembodiments of the present invention, the control of the pulse width maybe computed by a series of bit serial ORs or by performing a series ofbit serial Not-ORs.

It will be understood by those skilled in the art that for someapplications XOR gate 1232 may not be necessary. As an example, if thedata requiring the logical ORs is different than that for the processingthat would require the NOT-ORs then, for example, the data may beinverted before being stored in the ERAM. This pre-inversion may be doneon the backplane as it is being stored, by the input buffers to thebackplane, at some other place on the backplane, or the data requiringinversion may be sent to the backplane inverted.

In operation of slice 1202, an address (not shown) is generated toselect a location in the ERAM of the memory array (not shown) and a bitis output on data line 1218. Generally on the first cycle of amulti-cycle OR operation, control signal 1210 is zero so that theprevious state of the logic block D-flip flop 1226 is ignored and onsubsequent cycles, control signal 1210 is one/on to effect the logicalOR of its previous state with a next input on data line 1218 or itsinverse depending on control signal 1214. Control signal 1212 controlswhen the operation is performed and saved in logic block D-flip flop1226. There are generally one or more cycles that will be require tocompute an intermediate result stored in D-flip flop 1226. Theintermediate result stored in D-flip flop 1226 at the end of the one ormore cycles, may be the intermediate value 216 of the bit recursivefeedback shown in FIG. 2. Sometime after a bit wise OR intermediateresult is completed, output 1224 of logic block D-flip flop 1226 is sentthrough XOR gate 1233 to the MRAM enable buffer D-flip flop 1234 andlatched by clocking signal 1215 to produce the MRAM bit mask writeenable 1242. The output XOR gate 1233 will either be the output of Dflip flop 1226 or its inverse as controlled by Gobal_Out_INV signal1216. It will be understood by those skilled in the ART that thecombination of XORs 1232 and 1233 when controlled by signals 1214 and1216 may be used to perform a number of different bit serial logicalcombinations including a logical OR and a logical AND off all bits.MRAMs broadcasted write enable 1244, in effect, selects when bit maskwrite enable 1242 which is the output of the MRAM enable buffer is used.The data to be written in this embodiment is the same for all MRAMs andis broadcast to all MRAM inputs on M-DATA line 1248. The data is onlywritten in the case where both broadcast write enable 1244 and bit maskwrite enable 1242 are both logically a 1. What is written is controlledby a broadcasted data bit 1248. If the broadcasted data bit 1248 is a 1,then a conditional SET operation will be performed based on the state ofeach computed bit enable 1242. If the broadcasted data bit is a 0, thena conditional RESET operation is performed.

As will be understood by one skilled in the art, that there may be anynumber of ERAM read cycles between each control signal that saves theresult. There may be any number of bits OR'ed together over multiplecycles with the device shown. It will be understood that the logic shownis only an example and that various other logic and data buffering maybe used.

While the MRAM enable buffer D-flip flop (or bit) of processing elementillustrated FIG. 12 is not always be necessary, the storage D-flip flopallows a significant degree of timing flexibility between thecomputations from ERAM and the writing of results. Just one bit ofstorage can give considerable timing flexibility by combining it withcontrolling when to start operations from the ERAM and being able todefer the writing to the MRAM enable buffer bits and the write enable.It is noted that a bit serial OR operation of one embodiment of thepresent invention can take multiple cycles with the number of cyclesvarying based on the current “count.” when using the deductive comparemethod previously discussed. Without the storage D-flip flop that actsas output storage, the next operation may not start until the bit isused by the MRAM via the MRAM bit mask input. It is also understood bythose skilled in the art that there may be additional bits of outputstorage rather than the single bit i.e. the storage D-flip flop. Thesemultiple bits may be arranged in either a shifting arrangement or may beindividually selected to provide the data/control going to the MRAM.

It is also understood by one skilled in the art that while a singleinput from an ERAM goes to the PE, there may, via multiplexers or otherlogic, be other data from another RAM that may be applied to the PE.

Also shown in FIG. 12 is one bit 1252 of an input serial in to parallelout shift register and how input shift bit 1252 may be connected to thedata input. There may be many parallel bits being shifted at one timeand that there may be some selector/multiplexer circuitry that thechooses between the multiple bits to be driving as an input to data line1218. While in normal functional use, the data will generally flow frominput shift bit 1252 to the ERAM of the memory array via data line 1218,it is possible that read operations from the ERAM to the input shift bit1252 may also occur. It should also be understood that with additionalcircuitry, it would be possible for the PE 1206 to work on data directlyfrom the shift bit 1252 rather than having to wait for it to be storedin the ERAM first.

In some embodiments of the present invention, it is also possible thatseveral bits may be transferred in parallel to the ERAM though multipledata lines and multiple shift bits. In other words, there is notnecessarily a one to one correspondence between the number of PEs, theshift bit, and data inputs.

It will be understood by those skilled in art that the logical functionshown inside the logic block in FIG. 12 is only an example and that itwould be possible to perform other logical or arithmetic operations withdifferent logic and more control signals.

FIG. 13 shows a 1-bit wide “slice” 1302 of MRAM and ERAM input andoutput buffers 1304 and a PE (processing element) 1306 that supportsanother embodiment of the present invention. Bit lines 1308 indicated bya two-way arrow connect a memory array (not shown) to input and outputbuffers 1304 Global control signals 1310, 1312, 1314, 1315 and 1316,labeled as a group 1317 are sent to a series of PEs, of which PE 1306 isan example, to control operation of each PE. Generally all PEs along oneedge of a given memory array (not shown) will receive the same globalsignals.

ERAM of the memory array (not shown) acts as a conventional RAM and isaddressed with row and column addresses. However, the ERAM has a verywide output, nominally one bit per PE, and there may be as many as ormore than one PE per vertical or horizontal line of the display. Theother difference from a conventional RAM is that the ERAM may bephysically built interspersed with the MRAM as shown in FIG. 11.

Data line 1318 is 1-bit of output from the ERAM. control signal 1310,which acts as the Global PE Function control signal, selects theoperation for logic blocks 1320 and 1321 as shown by the dashed boxes.If different controls for blocks 1320 and 1321 are need, then therewould be multiple control signals 1310. If control signal 1310 is azero, then the output of AND gates 1322 and 1323 are a zero regardlessof the state of an output 1324 and 1325 and D-flip flop 1326 willreceive bit 1318 via OR gate 1328 and D-flip flop 1327 will receive theinverse of 1318 via inverter 1329 and OR gate 1330. If signal 1310 is a1 then the inputs of Flip flop 1326 will be the OR of its previousoutput with the value of bit 1318 and the input of flip flop 1327 willbe the OR of the inverse of signal 1318. Signal 1312 causes the outputsof the two OR gates to be latched by flip flops 1326 and 1327. In theconfiguration shown, both the OR and the NOT-OR of a series of bits online 1318 may be computed in parallel, which may be useful for someembodiments of the present invention. Multiplexer 1342 which iscontrolled by signal 1315 is use to select one of the two results to goto the MRAM bit mask enable bit 1343.

The output of multiplexer 1342 is sent through output XOR gate 1344 andthen latched into a MRAM enable buffer. The output or XOR gate 1344 willeither invert or not invert the output of multiplexer 1342 based on thecontrol signal 1316. D-flip flop 1354 under control of a global outputload signal 1314 to store the result of a series of operations. Theoutput of storage D-flip flop 1354 may be used to control the enablingof the MRAM write process as was described was described above withrespect FIG. 12.

The embodiment of the present invention illustrated in FIG. 13 supportstwo parallel computations using the same data coming from the ERAM. Thisarrangement may be used to support the MRAM arrays that don't support adirect write, but rather just setting or resetting of the MRAM bit. Inparticular it may be used when going from an LS-computed pulse width tothe MS-computed pulse width. Specifically the parallel path may be usedto conditionally Reset (turns off) the pulse if none of the MS bits is a1 where the main path conditionally Sets (turns on) the pulse if any ofthe MS-bits are a 1.

The only difference parallel logic blocks 1320 and 1321 is the invertingof one of the inputs by inverter 1329 in logic block 1321. In a sequenceof operations where the first step has the Global_PE_OR line, controlsignal 1312, off and all subsequent operations in the bit serialoperation have control signal 1312 on, the output of the first D-flipflop 1326 is a 1 if data line 1318 is a 1 on any of the steps, while theoutput of second D-flip flop 1327 is a 1 if line 1318 has a ZERO on anyof the steps. XOR gate 1344 may be used to affect output 1324 or 1325which is sent to XOR gate 1344 via multiplexer 1342. selecting which bitserial operation is used on a given cycle is determined by theGlobal_Sel line 1315 controlling multiplexer 1342.

It will be understood by those skilled in the art that other functionsmay be added and paths to memory may be supported in ways other than theways shown in FIG. 13 without changing the basic concept. Also, FIGS. 12and 13 each show “bit serial” operations of one embodiment of thepresent invention. However, many of the features of the presentinvention may be employed with bit parallel operations as well.

It will be understood by those skilled in the art, that having a verywide processor connected to a memory array may be used to facilitatetesting. It is anticipated that some functionality may be added to thePEs and/or their surrounding logic to support either or both test andself-test. For example, it may be useful to have the PE output a patternto save in the memory array and then perform a series of read and/orwrite operations and then use the PEs processing logic to see if thecorrect result is obtained.

FIG. 14 shows how a PE functionality, PE 1400, may be expanded tooperate on more complex functions than that of the PE of FIG. 12. PE1400 may be a bit serial PE or may operate on multiple parallel bits ata time. PE 1400 does not show the MRAM write back buffer bit of FIG. 12.

ALU 1401 is may be capable of doing arithmetic or logical operationswith its two data inputs 1402 that may be N bits wide (were N is 1 toany integer) and 1404 that may be M bits wide (M=1 to any integer) andwith the carry in input 1406. ALU 1401 may be a single bit wide to an Lbit wide (L=1 to any integer) result. For pure bit serial operationL=N=M=1. As is common with ALUs it may produce one or more “status” bits1408. For multi-precision operation including bit serial operation,result bit(s) 1406 are saved in latch 1414 with output 1416 and statusbit(s) 1408 are saved in latch 1418 with output 1420, each latch beingas wide a necessary to hold the bits.

Results that would control the write enable of the MRAM or which may beused for more general-purpose operations may be selected by multiplexer1422 to go to output lines 1424.

The output lines from the multiplexer may go directly to the MRAM, forexample, as bit write enables, or the output lines may be bufferedbefore going to the MRAM, or it may go out as data to memories otherthan the MRAM in a more general application of the hardware shown.

Inputs 1402 and 1404 are shown coming from input multiplexers 1426 and1428 respectively. The inputs to the input multiplexers shown are meantto just be examples. As shown, several ERAM data lines 1430, 1432, 1434,and 1436 from one or more ERAMs are connected to the input multiplexers.It should be understood that other memory or registers may also input tothe input multiplexers. Also shown going to the on of multiplexer 1426'sinputs is output 1416 of result latch 1414. Shown going to inputmultiplexer 1428 is a broadcast data bus 1442. For bit serial operation,the broadcast data bus might be one bit and for multiple bit operationit may be more than one bit. Broadcast PE Function 1450 has one or morecontrol signals that work to operate the ALU function, control theselection of the input by the multiplexers, and control the variouslatches.

The PE of FIG. 14 is intended to show how the PE function may beexpanded to do operations beyond just controlling the mirrors with themethods one embodiment. It will be understood by those skilled in theart, that the functionality may be augmented in many ways.

FIG. 15 shows an alternative implementation of an ERAM storage bit 1502that supports computation within a memory in accordance with oneembodiment of the present invention. The deductive counting methodpreviously discussed only requires that various combinations of databits be logically “OR” together which lends itself to simple logichardware implementations. FIG. 15 shows two SRAM bits 1504 and 1506 inthe same column and some transistors added to support a parallel ORoperation. It should be understood that there would be many rows andcolumns of such bits.

In addition to a common 6 transistors SRAM bit, an extra selecttransistor 1512 and pull down transistor 1514 are added to both SRAM bit1504 and SRAM bit 1506. This configuration prevents either bit 1504 or1506 from being overwritten by the “OR” operation. In normal operationthe row selects operate independently on bits 1504 and 1506. For the ORoperation, OR select lines 1516 and 1518 are both turned on at the sametime. It should be understood that lines 1516 and 1518 are just two ofmany ROWs of select lines in the memory array. If data line 1522 hasbeen previously precharged, then line 1522 is pulled down if either bit1504 or 1506 is a 1 and thus line 1522 will have the logical NOR (whichif inverted gives the OR function) of all bits that have their read ORlines on.

Assuming all bits on a set of column bits have the OR selects, variousbits as selected by the OR selects may be OR'ed together in a singlecycle. This has the advantage of allowing the recursive deductivealgorithm to require fewer cycles, as few as 1 cycle regardless of thecount if all the bit are in this type of memory, but has thedisadvantage of a more complicated ERAM storage. One embodiment of thepresent invention uses the multi-cycle OR approach in order to reducethe complexity of the ERAM.

It will be understood by those skilled in the art that FIG. 15 is onlyone example of ways to configure a wired OR function with an array ofbits.

While adding the OR function into the memory array adds some transistorsand/or complexity, it has the advantage of requiring only a single cycleto compute and only one discharge of the bit line which as the distinctadvantage of saving the overall power required to compute one or morepulses.

FIG. 16 shows a high level block diagram of an embodiment of a digitalbackplane 1602 of the present invention. A memory structure 1604contains the MRAM and ERAM bits 1606 mixed together in a large array1605, with ERAM ROW decoders and drivers 1612, MRAM ROW decoders anddrivers 1614, and bit lines 1616 going to the MRAM and ERAM sense ampsand drivers 1618. The ERAM data out and bit write mask to the MRAM havea wide bus 1622 connecting the ERAM data out and bit write enable mask(or in other embodiments simply data to the MRAM) to a linear PE array1624 of PEs 1626. Bus 1622 represents a series of connections betweenoutputs of the ERAM and MRAM 1604 and PEs 1626.

While a one for one connection is shown in FIG. 16, it will beunderstood by one skilled in the art that there may be multiplexers orother bus structures that may support various routings of data betweenmemory array 1604 and linear PE array 1624.

Input line 1632 to digital backplane 1602 go to a series of 1-bit wideserial-in, parallel out shift registers. There are a number of shiftregisters to support the data rate coming onto the device. The length ofeach shift register will typically be long enough to provide 1 bit forevery input to the ERAM. Once all the bits of input line are filled withincoming data, the shifting can stop. A backplane controller 1634 willselect (control lines not shown) one of the shift registers to send itsdata via lines 1636 to the write data input of the ERAM as controlled bythe row address 1638 and control lines 1640 to memory array 1604. Afterthe data from one shift register 1646 has been written in to, forexample, one row or a part of a row in memory array 1604, another one ofshift registers 1646 parallel outputs is selected on lines 1636 andwritten to a different location into the ERAM. For testing, lines 1636may also be used to read out bits from the ERAM and/or MRAM to put intothe shift registers 1646 and then the bits may be shifted out of shiftregisters 1646.

In some embodiments of the present invention, the write operations tothe ERAM will be scheduled at times when ERAM is not needed for readoperations. The controller can either directly schedule writes to theERAM from the shift register or other input structure, or it may simplygive an indication that there is a slot in time when write cycles arepermissible.

The address to where the incoming data is written may be computed on thedisplay backplane by controller 1634, or controller 1634 may have avalue on which the write address is based and can be computed off thebackplane and sent to it via line 1670. In some of the embodiments, thecomputation of the write addresses will be done in a circular bufferfashion.

It will be understood by one skilled in the art that a physical serialin and parallel out shift register is only one way to take in serialdata in and store it up to create a multi-bit wide write to a memoryarray. For example, a counter and static RAM structure is well known toprovide a similar function.

Expansion ERAM 1652 may also be used for data that many not fit in the“main” ERAM array inside the combined MRAM and ERAM arrays 1605 may beadded outside the arrays 1605. It may be advantageous to have dataoutputs 1654 of ERAM 1652 to be the same width as the output of the ERAMin memory array 1604 so as to support efficient routing to linear PEarray 1624.

While the bus connecting the other ERAM to the linear PE array is shownas being physically separate in FIG. 16, it will be understood that thisbus maybe a common bus with lines of bus going to the memory array 4. Itis also possible that there may be no ERAM inside of the display arrayblock of memory in the memory array and that all the ERAM may becontained in a block of memory outside of the display array.

An alternative embodiment of the digital backplane of the presentinvention similar to the digital backplane of FIG. 16 may have theExpansion ERAM have its own set of PEs that work in parallel with thelinear PE array. In this way parallel accesses may be made to reduce thenumber of cycles to make computations. This second set of PEs may beable to control the MRAMs bit enable mask or writes to the MRAM. In analternative embodiment, two sets of PEs may combine two sets of partialresults to control the MRAM.

Backplane controller 1634 generates the memory addresses and othercontrol signals for digital backplane 1602 including: row address 1638for ERAM and row address 1662 for MRAM row Decoder 1614, other ERAM 1652address(es) 1664, control lines 1640 for the MRAM and ERAM sense ampsand drivers as well as the broadcasted data 1606, PE control signals1668, and controls for the transfer of data from shift registers 1646 tothe ERAM(s). All or part of the data input signals 1632 may be providedto backplane controller 1634 by a data line 1670. These input lines 1632may be used to load registers or memory inside the controller. Controlor signals or codes within the data being received or by timing withinthe controller may specify when the incoming data is to be used by thecontroller rather than as data for display.

In a display application, a display cell will typically have at leastone MRAM bit in it that drives the output. Due to the row and columnnature of the MRAM memory, the display cells will be similarly organizedinto rows and columns. The configuration shown in FIG. 16, is designedto operate on an entire row of outputs at a time. Each time the MRAM rowis accessed generally one “count stage” is performed. For a simple pulsewidth there are 2^(M) count stages. For example for a 3 bit pulse widthcontrol there are 8 stages from 0 to 7.

In operation of a display, the controller will interleave accesses tothe various rows of the MRAM in order to control the various lines ofthe display. For every write to the MRAM rows there will be one or moreaccesses made into the ERAM to compute the next MRAM value. In oneembodiment of the present invention, there is one PE for every MRAMcolumn so that an entire ROW of the MRAM is computed at one time. Itwill be understood that it is possible to have more or few PEs and takefewer or more cycles for computations.

Assuming an equal number of MRAM columns, ERAM data outputs, and PEs asthere are columns of outputs, the controller will have to have at leastas many cycles of outputs as the number of ERAM accesses required forall the count stages for all the lines. This can result in more thanone-hundred thousand cycles for a typical display, having on the orderof one thousand lines of resolution.

There are thus multiple count stages that occur for multiple lines andeach of these count stages will generally involve one or more reads fromthe ERAM, one or more cycles through the PEs, followed by a masked write(as described with respect of FIG. 12) to an entire row of the MRAMstorage bits.

In many embodiments of the present invention, starting of the control ofthe counting process for each line is staggered so that only one line ofoutputs is controlled on a given cycle. For example the starting of thecounting may progress from the top to the bottom of the display image, aprocess known as “raster scanning.”

FIG. 17 illustrates one embodiment of a digital backplane 1702 inaccordance one embodiment of the present invention. In digital backplane1702, the ERAM is split into an upper ERAM 1712 and lower ERAM 1714 byhaving bit lines that only traverse half the height, and having separaterow decoders, upper E-row decoder 1716 and lower E-row decoder 1718,sense amps and drivers, MRAM drivers 1720 and 1722, and expansion ERAM1724 and 1725 on the top and bottom of MRAM array 1732. The MRAM isconfigured as a single array 1732 with MRAM bit lines 1728 running theentire height and upper ERAM bit lines 1730 and lower ERAM bit lines1732 running in this example, approximately half the height of thecombined arrays. There is a single M-row decoder 1734. Both MRAM drivers1720 and 1722 are capable of driving the MRAM but in operation only oneis selected to drive a given MRAM bit line at a time. Digital backplane1702 supports the ERAMs in both halves being used in conjunction withlinear PE arrays 1736 and 1738 to make computations in parallel and thensend their result to any row or some set or subset of rows in the MRAM.

As is common with data lines running between integrated circuits, a datainput 1742 may be running at a higher data rate per pin and/or that mayotherwise need some temporary buffering indicated by box 1744 to producedata input 1746 that enters digital backplane 1702. In some embodiments,buffering 1744 may also include some forms of processing that may rangeanywhere from simple bit inversion to more complex mathematicalfunctions that may do color space conversion and/or image scaling.Additionally some or all of the incoming data may be sent via lines 1748to the controller for uses similar to those for lines 1650 in FIG. 16.The buffered data in this embodiment is split into 4 data streams 1746that will eventually go to 4 multi-bit wide serial-in by parallel outshift registers 1752, 1754, 1756 and 1758. The shift directions of thevarious shift registers may be different (some may shift left wereothers shift right toward the center of the device) and thus the datawill need to be ordered properly either when sent to the device or bybuffer 1744. Digital backplane 1702 includes four look-up table blocks1762 each containing one or more color look-up tables. Timingre-synchronizing latches 1764 may be used as necessary to buffer thedata and keep the data synchronized with a system clock as signals skewacross the backplane. A backplane controller 1766 generates separateaddresses for the Upper and Lower ERAM 1712 and 1714, Expansion ERAM1724 and 1725 (address lines and row decoders and other buffering is notshown in FIG. 17 for simplicity), and functional control and broadcasteddata for linear PE arrays 1736 and 1738 (the control signals are notshown). Backplane controller 1766 is connected to the Upper ERAM rowdecoder 1716 by data line 1772, is connected to row the Lower ERAM rowdecoder 1718 by data line 1774, and is connected to M-row decoder 1734by data line 1776

For simplicity the various paths between the PEs and the ERAMs and MRAMsare not shown.

Each look-up table may contain one or more RAM arrays that are used totranslate the data value going in to a potentially new value going outby table lookup methods that are well known in the art. The values intables are set to adjust for various factors such as the response of thedisplay device and the human visual response. These tables are commonlycalled “gamma correction tables.” The time through the table lookups maytake one or more clock cycles. These look-up tables are also optionalfeatures and some embodiments of the digital backplane of the presentinvention do not include the color look-up tables of FIG. 17.

Each block of look-up tables may contain multiple look up tables withinthem. There are several reasons for multiple lookup tables. One reasonis that the data rate may be too high to be sustained by a single lookuptable and so two or more parallel lookups may be provided. In the casewere the device is being used for multiple different colors, for exampleRed, Green and Blue, it is common to need to have different lookuptables for each of the colors.

FIG. 17 illustrates only one of many configurations of the architectureof a digital backplane of the present invention and demonstrates anumber of potential enhancements.

In a method in accordance with one embodiment of the present inventionfor driving output arrays with recursive feedback, there are generallymore accesses needed to the ERAM array for computing the next partialresult that uses a masked write to the MRAM. The digital backplane ofFIG. 17 thus supports an average of 2 accesses to the ERAM for eachwrite to the MRAM. By cutting the ERAM bit lines approximately in halfwill also improve their inherent electrical performance as the bit lineswill have half the loading. It may be desirable to have more ERAM bitsper column than MRAM bits as shown in FIGS. 11A and 11B and thus lowerthe loading of the bit lines relative to the loading of the MRAM bitswould be advantageous. Furthermore where the MRAM read speed may beunimportant for the function operation of one embodiment of the presentinvention, the ERAM read speed may limit the overall performance of thedevice.

The digital backplane of FIG. 17 also allows data values associated witheither the upper or lower part of a display to be stored in either theupper or lower ERAM regardless where in the MRAM they will affect. Itsome embodiments, it may be preferable to store all the bits associatedwith a given ROW in MRAM to be stored in the same ERAM so that they canget to the same PE array.

In some embodiments of a digital backplane of the present invention, itmay be desirable to have different lookup tables at different times forthe same color values. These multiple lookup tables may be stored andswitched between. One use of such multiple look-up table would be toperform “temporal dithering” to break up or reduce certain types ofartifacts. One type of artifact that temporal dithering may correct arethe artifacts caused by lateral fields that affect LCoS devices.

It should be understood that the lookup tables used for correctingdisplay would generally have more outputs than inputs. For example, itis common to take an 8-bit pixel value of one of the Red, Green, or Bluecomponents and send 8-bits as an address in, to a memory 10 to 12 bitswide to get a 10-bit to 12-bit output. Thus more data bits come out ofthe table than go into it and so by moving the look up tables onto thebackplane, the data needing to be sent to the backplane is less. In someembodiments, it may not be possible to do the table lookups on thebackplane and in which case these table lookups may be done in anexternal device. In some embodiments of the present invention a deviceknown as a “Panel Interface” or PIF will be used to help manage externalmemory, perform color table lookups, and other functions it can off-loadfrom the panel. The PIF may also compute some or all of the addressesfor the writing to the ERAM and send values for the backplane controllerto base the addresses on for writing to the ERAM.

The four shift registers in FIG. 17 support a lower data rate forshifting data in. The shifting in from the left and right sides maysupport a more compact device layout, although it is not absolutelynecessary. The data going to the shift registers from the input and thedata buffering comprehend the shift direction.

The shift register may load either the ERAM mixed with the MRAM or theExpansion ERAM. In some embodiments, it would also be possible that theshift register would load the PEs directly. As has been previouslymentioned, there are other alternatives for distributing the data toinput of a very wide memory other than shift registers, such as using abroadcasted data bus and latches on the inputs to the wide memory suchas with the ERAM.

In one embodiment, a digital backplane of the present inventioncontrolled by a programmable program instruction sequence. Thisinstruction sequence may be stored in RAM so that that the instructionsequence would be reprogrammable. However, the instruction sequence maybe partially or totally stored in a ROM. Also, many or all of thecontrol sequences may also be generated by dedicated hardware.

The image generation of some embodiments will be in raster fashion as iscommon in the display device art. A raster process generally starts ateither the top or one side of the display and works its way from top tobottom. As will be understood by those skilled in the art, the directionof the raster scanning is somewhat arbitrary and may be from bottom totop, or even left to right or right to left. So for a top to bottomraster process, the processing starts with the top line and progress tothe bottom. There are also raster processes, such as “interlaceddisplays” where there are two fields wherein the even lines areprocessed on one field and then the odd lines processed on the next. Itwill be understood that the concepts of the present invention may beapplied non-sequential raster processes such at interlaced displays oreven to non-raster processes as the application may require. For thepurpose of simplification, a simple top to bottom sequential rasterprocess for a single field and single color will be described below.

Also, while the processing for the first line will start first, theprocessing of other lines occurs concurrently, but each subsequent lineof the display's processing delayed by the time between lines of theraster process. Also, in the processing of an embodiment of the presentinvention, many lines if not all the lines will be in some stage ofprocessing concurrently. The issue for the instruction program andsequencing is to support the concurrent programming to perform thenecessary pulse control for all the lines.

The concepts of the present invention can also be extended to supportvarious forms of sequential color operation. It is a common practicetoday to use a single microdisplay and shine multiple colors of light onit in sequence at a rapid rate to generate a color image. A common formis to have a rotating color wheel with various, usually primary, colorsallowed to pass through it. Between each color there is a blank/darkarea or “spoke”. As the color wheel rotates, a blank band caused by thespoke blocks the light, followed by a given color, then another spokeand another color and so forth as the wheel rotates. The rotation of thewheel causes a given color to sweep across the display in a rasterfashion. In this case, the raster processing would follow insynchronization with the rastering of the microdisplay by the lightfalling on it. Field sequential color operations generally occur a muchhigher rates to display 3 or more colors and prevent the eye detectingthe breaking up of colors so the processing much occur at a higher rate.Also, depending on the blanking/spoke time, there may be a one time afirst color finishing, a spoke, and a new color starting to illuminatethe display all at the same time.

In field sequential use, it is also common for the various colors to beshown for different amounts of time. This can also be supported with theconcepts of the present invention, by supporting the control changesbetween various color fields as they occur in sequence.

A more recent form of using a single microdisplay to support more thanone color is known as “color scrolling.” In this form, generally 3 ormore colors are scrolled across the microdisplay at the same time withblanking areas separating them. Scrolling color is also a raster processonly with multiple rasters occurring simultaneously but separated intime. Scrolling color can also be supported applying the concepts of thepresent invention by having more pointers being kept track ofsimultaneously.

Both the rotating wheel sequential and scrolling sequential processesare inherently raster processes and fit well in the raster scanningprocessing. Another way of generating sequential color is “flashingsequential color.” This form of flashing sequential color is often usedwith Light Emitting Diode illumination, most commonly in near eyeapplications but may include color light sources that are bright enoughto support projection displays. The flashing sequential colorillumination is not an inherently raster process as all parts of thedisplay are illuminated or not at roughly the same time. This type ofdisplay illumination can also be supported with the concepts of thepresent invention by adding support to generate an “initial condition”for all the mirrors during the blanking interval and then turning offall the mirrors at blanking time. This would in effect split a singlepulse for each line into two pulses. Once the initial condition isestablished, each line would be at a staggered starting point in theirsequence. The once initially the control method may be very similar tothat which will be discussed with respect to FIGS. 18, 19, 20, and 21.

To support the flashing sequential color (or flashing field), it may bedesirable to have a mechanism to quickly establish the initial stage ofthe mirrors. One embodiment would be to have the master-slave typestorage bits in the MRAM. In one embodiment the MRAM master-slave typeof bit design may support the master-slave operation for quicklyinitializing and/or clearing the slave (which would be the drive bit)and at other times the master part of the bit may be randomly accessedand used as for other purposes such as ERAM. In this embodiment, the bitwould have both random access and master-slave accesses.

In order to explain the processing, some very simplified examples areshown in FIGS. 18, 19, 20 and 21 that keep the tables manageable insize. The simple example will assume a dual pulse control with only 2Least Significant (LS) and 2 Most Significant (MS) bits controlling adual count, single pulse width for a single field. This would supportonly 16 gray scale levels in this simple example. The concepts shownhere can, however, be extended to any number of bits per LS and MS bitsas well as to various forms of field sequential operation. Furthermorethe LS bit Times and the number of clock cycles between lines will bekept very small for this example.

In following through this very simple example, it should be realizedthat in a real system with over 1000 lines of display with 10-bits pergray scale, split with 5-LS and 5-MS bits there may be over 100processor clock cycles in the time of one LS-bit of intensity time andthere will be over 100 processor clocks between line starts.

The control of one embodiment of the present invention has bit serialprocess for each setting or resetting step of the display mirrorassuming a masked write mirror array. The process assumes that the LSbits are controlled by a delay until starting based on the LS bits andthen the pulse stops based on the MS bits. This in turn means that theLS bit processing is effectively a countdown process, while the MS bitprocessing is a count up process.

For examples of FIGS. 18, 19, 20 and 21, a roughly binary weight may beused, but, the concepts shown may be extended to any form of weightingof the bits in terms of time. With binary weighting, the “LS-bit time”is the time difference between two pulses differing in value by 1 LS-bit(bit 0). With simple binary weighting, the time between 0 and 1 is thesame as between 1 and 2 or 2 and 3 or any other difference of 1.

It should be noted that FIGS. 18, 19, 20 and 21 only show up to time=63cycles of a frame. This is only enough cycles to show the start of theprocess.

For the very simple examples shown in FIGS. 18, 19, 20 and 21, theLS-bit time is 4 clocks. This time is chosen to show the working of thescheduling and is very short. In a typical system the LS-Bit time wouldlikely be over 100 clocks. Thus the time difference between processorclocks in a typical system may be less than 1% of an LS-bit time, whilein the simple example with only 4 clocks between LS bit times time is25% of that of an LS bit time. The LS bit time would be a function ofthe clock frequency of the processor, the number of bits of precision inthe time of the pulse, and the length of time for one field.

The time between line starts in terms of processor clocks for a givenfield acts as a base frequency for memory events in the processing andthe operations to be performed. In the first example, illustrated intabular form in FIG. 18, the time between line starts of the rasterscanning process is 17 clocks. This time is a function of the timebetween raster lines in a raster scanning process and the processorclock rate. There needs to be enough clock cycles between scan lines tosupport the, MRAM write cycles, the ERAM read cycles, and time slots tosupport writing new incoming data to the ERAM (for example in a circularbuffer fashion). The number of clocks for the LS-bit time may be more orless than the number of clocks between lines. The more the number oftime clocks cycles between lines exceeds the number needed for MRAMsetting or resetting events, of ERAM read and write events, the easierand more flexible the scheduling, but also the higher the clock rate ofthe processing and perhaps the more program memory may be required.

There is a “process” for every time step and then each of theseprocesses will be programmed to run concurrently but offset in time. Inthe simple example illustrated in FIG. 18, the LS-bit require 3 timestep processes or “counts” with the two bits supporting a LS-Pulse widthof form 0 to 3 time intervals wide. In this example the 2 MS-bitsrequire 5 time step processes. There are two more steps in the MS bits,one at the start for the assumption of a memory array that can only beset or reset and one at the end to assure the pulse is turned off.

In one embodiment of the present invention a line of mirrors on a givenline is processed in a single step. Note it is possible to process 2 ormore lines at the same time if there is parallel hardware to support it,but the following simple example will only discuss a single line beingoperated on at a time. The process described works in a raster fashionworking from the top line to the bottom. Other processes may also besupported with different programming.

The table of FIG. 18 shows the time intervals for a 2-LS and 2-MS bitdual count with a single pulse algorithm with a LSB time of 5 clocks anda line time of 17 clocks. Under the LS MRAM heading are the 3 time stepsfor the LS Counting and under the MS MRAM heading are the 5 time stepsfor the MS pulse width control. For each process that controls the MRAMthere are zero to 2 bits that must be read from the ERAM per thedeductive compare algorithm that is another aspect of the presentinvention. The LS ERAM read and MS ERAM read heading and the columnsunderneath them, correspond to the columns under the LS MRAM and MS MRAMrespectively.

Where the MS process steps/counts uses a series of “count up deductivecompares” as was previously described with respect to FIGS. 3 and 4, theLS process will use a variation of that process, with “count downdeductive compare” to delay the start of the pulse. Where the count updeductive compare process looks for bits corresponding to the 0's in the“current count,” the countdown process looks at bits corresponding to1's in the current count and instead of OR'ing together the valuesfetched, it logically ANDs the bits together to determine whether towrite (control the bit write enables or other process to selectivelyupdate drive bit). A logical AND is the same as inverting all the Inputsand inverting the output of an OR or by some other logical equivalent.

It should be understood that the descriptions will assume that a “1”written to a drive bit turns a pulse “on” and that a “0” to a drive bitturns the pulse off. It will be understood by those skilled in the artthat with various display devices or even the same display devices, suchas LCoS devices requiring “DC restoration,” that the logical sense ofwhat logic level turns a light modulating element “On” and “Off” may beinverted. These well-known necessary inversions of the data to maintainthe proper drive orientation are assumed to be done by hardware orsoftware programming.

The ERAM bit numbers given in the table of FIG. 18 correspond to the bitposition (0 to 3 in this case) of the given read that is associated witha given mirror. Also, that, for example, line 1, a given bit number willbe stored in a different memory location than that same bit position forline 2. In one embodiment of the present invention, the bits are storedin memory so that all the bits corresponding to one bit position forevery mirror in a line of the display are fetched in a single access. Inone embodiment of the present invention, the ERAM bits corresponding toa given bit position will be stored in circular buffers rather than atconstant or fixed memory address. In one embodiment of the presentinvention, each bit position will have its own circular buffer and thelength of each buffer will be long enough to hold the bits for all linedneeding those bits. Conceptually with circular buffering, the bitposition will specify which circular buffer and the Line Count for theMRAM (the number in each time clock under the LS MRAM or MS MRAMcolumns) would in effect index into each buffer. The Count numberheading is the value of the current “count.” Note that there is nophysical count that is being compared against, this is just the timeinterval. Also, that the LS count down from 3 to 1 where the MS count upfrom 0 (two zero “counts” as will be explained) to 3.

The Binary T Weight row shows the time value for perfectly binaryweighted pulses, in this case of time equal to 4 clocks. The “AdjustedTime” row is the time value that is actually used. In this first exampleillustrated in FIG. 18, the adjusted time will be the same as perfectlybinary weighted time. The Offset row will show the number of clockcycles that a set or reset interval is delayed relative to perfectlybinary weighted time in the case of MRAM setting or resetting, or thenumber of cycles a ERAM read process is scheduled ahead of the writeprocess.

In the simple example of FIG. 18, it is assumed that the MRAM may be setor reset on the clock cycle immediately following the last ERAM readthat is necessary. In a practical system it may be necessary to schedulethe read process further ahead depending on the relative times of theread and write processes and the time of the bit serial processing andother hardware considerations.

The row in the heading of the table in FIG. 18 labeled “Set/Reset Disp.”has and “S” for if the process will set (turn on) the display or an “R”to reset (turn off) the display. NOTE: It is assumed that the previousfield has ended with a step that assures that the mirrors are turned offand thus their state is known.

The far left column after the headings in the tables corresponds to agiven clock time of the processing. In this example, Time=0 isarbitrarily set to be when the first conditional set of the zero'th(top) line occurs. For the subsequent descriptions, the time in the lefthand column will be used in referring to a given row in the table.

In the upper right side of the table of FIG. 18, the LSB Timecorresponds to the number of clocks in a binary weighted time (in thiscase 4) and the Line time corresponds to the number of clocks in a linetime (in this case 17).

The four right hand most columns are used to track which processes arepotentially writing or reading for each cycle and to show if there is aconflict. Each “digit” in the multi-digit numbers may be a 1 or 0 in thewrite Pattern or the read Pattern and corresponds to the processes stepcolumns in order from left to right. If the whole value is “0” thenthere is no operation going on in that cycle. If there is more than asingle “1” set in the pattern, then there is a conflict as indicated bythe respective write conflict and read conflict. For the first exampleof FIG. 18, there are no “write conflicts” but there will be asdiscussed a read conflict for every line interval.

Sometime before time=0, the all the mirrors on line 0 are assumed to beoff (for the purposes of this description writing a logical 0 to themirror is assumed to turn it “off”). For a 2 bit LS bit count process ofthe start of the pulse will be delayed from 0 to 3 LS-time intervals. Inperforming LS Count Step 3 (the first count step in the LS count downprocess), if and only if both LS-bits corresponding to a given mirrorare 1, will a given mirror be SET (turned on), this corresponds tologically ANDing bits 0 and 1 associated with a given drive bit in agiven line of spatial light modulating elements. Using a deductivecompare count down process, both bits 0 and bit 1 corresponding to thepixel of a given mirror must be fetch as shown in the LS ERAM readsCount 3 column in the table. With the bit serial processing, it willtake 2 cycles to read both LS bits at time=−2 and time=−1 as shown. The“SET” condition is the logical AND of the two bits as may be done by thelogic shown in FIG. 12.

In subsequent count processes, one or more ERAM bits read and processedby the PEs before the conditional setting of the mirror may beperformed. In FIGS. 18, 19, 20, and 21, the LS and MS MRAM write columnsshow the Line that is being written and the LS and MS ERAM reads columnsshow the bit locations that are read out of buffers preceding the MRAMcondition set or reset process.

Since there are 17 clock cycles between line starts in the example ofFIG. 18, the processing of LS RAM Count 3 for line 1 occurs 17 cyclesafter the same process occurs for Line 0. All other line count processesfor Line 0 of the output will also occur 17 clock cycles later in thisexample.

In these examples the same bit position are fetch but for different linenumbers separated by the Line Start Time rate (17 cycles for FIG. 18).The process shown is “deterministic” (occur at regular intervals) butother well-known processes may be used that are less deterministic, suchas methods based on keeping a buffer full.

In some embodiments, the ERAM bits will be constantly reallocated suchas with a circular buffer reallocation method. Thus the memoryallocation process is constantly computing the physical address of wherethe ERAM bits are stored and so bit numbers under the LS and MS ERAMread columns give the bit position and may not be directly used as anaddress in some embodiments.

The time of an LS bit time interval is given as being 4 Clocks. It willbe noted that at LS Count step 2 the mirror bits on line 0 are going tobe conditionally set at time=4 or 4 clock cycles after the conditionalsetting process at time=0. Thus if the pulse is not set at time=0 and isset at time=4, the pulse will be 4 clocks narrower, the LS-bit time.Using the deductive compare of the present invention, on bit 1 of thetwo bits needs to be read as show at time 4 under the ERAM reads. Ifthis bit is a 1, then the corresponding MRAM bit is set (turned on).Note that is might be a redundant setting of the bit depending of thestate of bit 0 of the corresponding MRAM bit in a process similar tothat shown in FIG. 4. It will be noted that this same count step processfor count 2 repeats for Line 1 17 clock cycles later.

Furthermore, after LS count step 2 when bit position 1 of line 0 is readat time=3 bit position 1 of line 0 is never read again. Thus the memoryassociated with this location may be reallocated. Subsequently aftertime=7, bit 0 of line 0 is never read again and may be reallocated.

On LS time step 1, line 0 is conditionally set at time=8 or 4 countsafter it is conditionally set at time 4. In this case bit 0corresponding to a given mirror is read at time=9 and if it is a 1, thenthe corresponding mirror will be set. If the mirror is already set, aredundant setting will have no effect on the mirror output.

The beginning of the MS control controls the end of the LS pulse in thisexample. In the example of FIG. 18, it is assumed that the MRAM arraysupports only setting or resetting and cannot be directly written. If itmay be directly written with a value, then this two-step processdescribed below may be done in one step. At time=12, or 4 clocks afterthe LS time step 1, the mirror is conditionally RESET (turned off). Thereset condition will be if all MS-bits are zero (in this case, the 2 MSof 4 bits being bits 2 and 3) in which case there will be no MS pulsewidth. While for a true “single” pulse, this the conditional resettingis necessary, in practical terms, this resetting may also be doneunconditionally since it would be a very narrow pulse (for example, aclock cycle or two later) followed by a conditional setting of the bitas in a real system the time between writes may be so fast as to causean insignificant visual effect (and thus may be considered to be“substantially a single pulse.”) As shown at time=13 the mirrors forline zero are conditionally set if ANY of the MS bits (bits 2 or 3)corresponding to a given mirror are a 1. This conditional setting makesure that if the pulse is not turned on by the LS-bits if, for example,all the LS-bits corresponding to a mirror is zero, or if the pulse isunconditionally turned off at the end of LS-bit time, that the mirrorwill start Set (ON) if any of the MS bits are a 1.

The MS ERAM reads bit 2 of line 0 at time=10 and bit 3 at time=11 intime for the conditional reset of the bits on line 0 at time=12. If anunconditional reset method is used, then these bits may be read oneclock cycle later. In the conditional reset of this example, it isassumed that the PE has the ability to process the effective AND and ORof the bit serial operations in parallel as shown FIG. 13 so that thebits only need to be read once which produces the control for theconditional reset and set.

For binary weighting with 2 LS bits (bits 0 and 1), each MS time stepwill be 4 times the LS bit time or in this case 16 (4×4) cycles. Thus MSbit time step 1 for line 0 occurs at t=12+16=28. It will be noticed thatif all of the LS-bits (bits 0 and 1) are all zero, the pulse will go upat T=13 and thus the first MS count will be one “short,” but in a realsystem with on the order of 100 cycles per LS-bit time, this would be aninsignificant time and visual difference (less than 1% of an LS bit).

At MS time step 1 only bit 3 is needed due to the deductive comparemethod. But it will be noted on the “uncorrected” timing chart thatthere is a read conflict between this read and the read for step 0 ofbits 2 and 3 associated with line 1.

Referring now to the Corrected time chart in the table of FIG. 19, itwill be noticed that read of bit 3 for process for the MS processingstep 1 is move back from time=27 in FIG. 18 to time=26 in FIG. 19. Butthis would have conflicted with MS Step 2 read of bit 2 in lateroperation (for example the MS read in time step 3 that occurs first attime=43 in FIG. 18), so MS Step 3's bit 2 read will also be moved backin time by 1 cycle. The changing in the timing from binary weighting isshown on the Line “Offset” in FIG. 19. This is the reason for the forthe write back buffer that has been shown associated with the variousPEs. The reads and processing may be performed earlier and stored in thewrite back buffers. There may be more than one write back buffer bitallowing even more freedom of the placement of the reads relative to theset/resets. The set and reset operation controls the mirror's on and offtime. The ERAM reads just need to be performed enough in advance to haveprocessing completed before it is needed for the set/reset process. Thesimplistic method shown in the uncorrected tables is to schedule theERAM reads immediately before the writes, an alternative method would beto schedule the reads in the order they are required until the buffergoing back to the MRAM will be full or in other words schedule the ERAMreads and the PE processing as soon as possible without to the limits ofthe write back storage.

Continuing on with the “corrected” timing for the conditional resettingof MRAM bits on Line 0 at MS Count Step 1 in the table of FIG. 19, ifbit 3 for the corresponding MRAM bit on line 0 is a zero, then the pulseis reset. After bit 3 for line 0 is read in the MS processing step 1 attime=26, it is never used again and thus physical memory associated withthat bit position storage buffer may be reallocated.

Going on to MS count step 2 for line 0 at time=42, bit 2 is read and ifthis bit is a 0, then the corresponding mirror is reset at time=44. Thebuffer for bit 2 for all the mirrors on line 0 is no longer needed aftertime=42 and therefore can thus be reallocated.

In FIG. 19, MS processing count step 3 simple resets the pulse to offregardless of the ERAM bits. In this case the pulse would only be on ifboth bits 2 and 3 were both 1 thus causing the pulse to not be resetbefore the end. This is the last step in processing a given line ofmirrors. This time may or may not be near the end of the display timedepending on the number of lines, the number bit counts, the number ofclocks per Line Start, and other variables associate with the lightmodulation. In some cases, particularly for (non-flashing) fieldsequential and scrolling color operation, there will be a blanking timebetween fields. For a 3 panel system with a constant light source orlight modulating elements not needing a blanking time (such as DLP™),there may be very little time between the end of one field and thebeginning of the next. At the top of the timing table, there isrelatively little activity in the MS bits. If in fact this is a displaydevice and there is little or no blanking time, the end of the previousfield would be processed in these “empty” slots as the process iscontinuous.

While the time steps for the MS process is different than the LSprocess, the time between lines is a constant, that being the clockcycles between line starts which in this example is 17 cycles. Thusthere is a periodicity or repeating pattern at the rate of the number ofclocks between lines. Thus for example the condition reset of line 1occurs exactly 17 cycles after the conditional reset for line 0 and 17cycles before the conditional reset for line 2. In fact all the readsand sets/reset follow a constant pattern. This fact may be used togreatly simplify the control process. Conceptually the program for the“line time” will be the “inner loop” of the control.

The table of FIG. 20 shows an uncorrected example for an LS bit time of4 clocks and a line to line spacing of 13 clocks. Uncorrected, there areperiodic conflicts with some of the reads and some of the writes.Looking at the corrected table of FIG. 21 the write conflicts have beenresolved by delaying the MS step 0 setting by 1 clock and subsequentlydelaying MS steps 1, 2, and 3 by 1 as well. In a real design with 100'sof clock cycles, the slight delays to avoid conflicts will beinsignificant.

In a more realistic system with, for example, a single field (forexample a 3 panel system) with 10-bits split into 5-LS and 5-MS bits,there will be 31 LS program steps and 32 MS processing steps (counting“step 0” as one step). With the deductive counting method, there will bethe need to read half of 5 bits, 32 times for each of the LS and MSprocessing. This would be 2.5×32=80 LS ERAM read cycles and 2.5×32=80 MSERAM read cycles plus cycles to allow for writing if the ERAM is singleported. Assuming a single ERAM structure that reads one line of ERAMbits per cycle, there would need to be at least 80+80=160 clock cyclesbetween lines and preferably more than that to support flexiblyaddressing access conflicts and writing to the ERAM. In this example,there would be about 64 conditional sets or resets to the MRAM or morethan 2.5 Cycles per set/reset thus allowing for flexibly avoiding writeconflicts.

In the examples described above, it has been attempted to approximate abinary weighted timing for the various counting steps. In one embodimentof the present invention, the various steps will be a sequence of readsfrom a memory array. The time between steps can thus be programmed toany amount and not necessarily binary weighted in time.

In the examples described above, the ERAM read process isfixed/determinist. It will be understood by those skilled in the artthat it is only necessary that the ERAM read cycles be completed in timeto complete the PE computations before the corresponding MRAM cyclesoccur. Thus it would be possible rather than to have a fixed programprocess for accessing the ERAM to have a process where ERAM cycles arescheduled to keep a MRAM updating buffer full. It is also possible thatthe write process may be non-deterministic so long as it meets a certaintolerance. Even if the processes are non-deterministic, they will tendto have a periodicity related to the line start rate.

It will also be understood by those skilled in the art that while aprocess that is repeated one per number of line counts is shown, thesequencing may be related to some multiple or sub-multiple of the linestart rate.

There are cycles where there is no ERAM reads. Assuming the ERAM is asingle ported RAM structure, these would be times in which write cyclesto the ERAM may be performed in order to update them with new incomingdata memory locations that have been reallocated.

FIG. 22 shows a system 2200 with a panel backplane 2202 of oneembodiment of the present invention. Only some high level blocks forsome of the function blocks of backplane 2202 are shown, including theMRAM and ERAM array 2204, two blocks with a shift registers and a lineararray of PEs 2206, the backplane controller 2208, an input buffer 2210,that receives input pixel data and control signals 2232 to the system.The backplane 2202 may have any of the features of the previouslydescribed embodiment including but not limited to additional ERAM, ColorLookup Tables, and processing in the Input Buffer. Only some of the datapathways are shown in FIG. 22 including the data pathways between theshift registers and PEs and the MRAM, the pixel data Input to the inputbuffering, from the Input Buffering to the backplane controller, andfrom the input buffering to the PEs and shift registers.

FIG. 22 shows a system where the panel accepts the pixel data withoutthe need for extra external data storage. The pixel data in its originalformat is processed on the display. There may be table lookups, colorspace conversion or other processing done to the incoming data in theinput buffer and/or the PEs or other hardware present on the backplaneincluding plane splitting or other reformatting of the incoming data.The pixel control signals may be used to synchronize the display.Instructions and other data and control information may be sent to thebackplane and the backplane controller

FIG. 23 shows a system 2300 with a high level block diagram of the panelbackplane 2302 of one embodiment of the present invention. Only somehigh level blocks for some of the function blocks of backplane 2302 areshown, including the MRAM and ERAM array 2304, two blocks with a shiftregisters and a linear array of PEs 2306, the backplane controller 2308,an input and output buffer 2310, and Input pixel data and controlsignals 2332 to the system. Included in FIG. 23 is an external memory2334 which may be a DDRAM or other suitable memory and may be one ormore physical device, with its data bus 2334 and address and controlsignals 2338.

The backplane of FIG. 23 may have any of the features of the previouslydescribed embodiments including but not limited to additional ERAM,color lookup tables, and processing in the input buffer. Only some ofthe data pathways are shown in FIG. 23 including the data pathwaysbetween the shift registers and PEs and the MRAM, the pixel data Inputto the input buffering, from the Input Buffering to the backplanecontroller, and from the input buffering to the PEs and shift registers.

The system of FIG. 23 differs from the system of FIG. 22 in that thereis external memory storage used. Generally the bandwidth over data bus2336 will be substantially less than that which is available between theMRAM or ERAM and the PEs on the backplane and this may be a significantconsideration in storing data off the backplane in memory 2334. Thebackplane controller in addition to controlling the backplane itself,also controls, including generating address for the external memory. Thesystem of FIG. 23 may be advantageous to take advantage of therelatively low cost of memory devices versus the cost, includingtesting, of memory on the backplane. The backplane's controller andinput/output buffer will likely do some form of reformatting the dataincluding “plane splitting.”

FIG. 24 shows a system 2400 with a high level block diagram of the panelbackplane 2402 of one embodiment of the present invention. Only somehigh level blocks for some of the function blocks of backplane 2402 areshown, including the MRAM and ERAM array 2404, two blocks with a shiftregisters and a linear array of PEs 2406, the backplane controller 2408,an input and output buffer 2410, and data and control signals 2422 froma panel interface 2423. Panel interface 2423 may also send data andcontrol signals 2424 and 2426 to other backplanes, for example in a 3Panel system panel interface 2423 may send data and control to 3backplanes that have be made into display panels. The panel interfacetakes incoming pixel data and control 2432 from the rest of the systems,and sends some or all of the pixel data, perhaps reformatted, to theexternal memory 2434 via data lines 2436 and the PIF generates controlsignals and addresses 2438 for the memory 2434. It will be understoodthat the memory 2434 along with its controls, addresses and data linesmay in some embodiments of the present invention be integrated into thePanel Interface 2423. The panel interface may include data buffer/memoryand control logic to reformat or otherwise manipulate the data.

Included in FIG. 24 is an External memory 2434 which may be a DDRAM orother suitable memory and may be one or more physical device, with itsdata bus 2434 and address and control signals 2438. The backplane 2402may have any of the features of the previously described embodimentincluding but not limited to additional ERAM, Color Lookup Tables, andprocessing in the Input Buffer. Only some of the data pathways are shownin FIG. 24 including the data pathways between the shift registers andPEs and the MRAM, the pixel data Input to the input buffering, from theInput Buffering to the backplane controller, and from the inputbuffering to the PEs and shift registers.

The PIF can also handle many of the processing tasks that wouldotherwise need to be performed on the backplane. The PIF controls theexternal memory and may perform reformatting including plane splittingof the pixel or other data. The PIF may manage the write bufferingprocess including generating circular buffer addressing of where tostore incoming data. The PIF may generate and send to the backplaneother control information. The PIF may also download newinstructions/programs or other control information for the backplanecontroller to use. The PIF may be implements in many ways including acustom ASIC or FPGA has are common today. There may be internal orexternal non-volatile storage such as an EEPROM that can hold the datathat programs and FPGA, data for color lookup tables and can hold theprograms or other control information that may be sent to the backplaneand its controller.

Color scrolling sequential requires tracking each color fieldsimultaneously. The starting time of each field will be offset so thatthe various fields are working in a different part of their displayprocessing. Thus there would need to be a set of control steps for eachfield. Thus for a 3 field scrolling color system, number of read andconditional write cycles would triple. The timing for the various fieldsmay be interwoven into a single program flow. The various fields mayhave differing timing (clock cycles between time steps), to, forexample, compensate for a color spectral light deficiencies in aparticular light source. In order to keep the ERAM access requirementand thus the processing clock, from going too high, the ERAM may besplit in two with two sets of PEs. This would halve the ERAM accessrate. In one embodiment of the present invention with a split ERAM, theMRAM would still be accessed as a whole and written. In order to keepthe processing load from being too high side of the ERAM or the other,it might be desirable to stripe the processing so one ERAM and set ofPEs processes the even lines and the other ERAM on set of PEs processthe odd lines. It is also possible that the MRAM array may be split insome manner such as being split into top and bottom arrays or “striped”with every other line in a different array.

In the deterministic methods shown, the number of clock cycles betweenlines is the same for the various fields in field sequentialprogramming, even if the various fields last for different amounts oftime. Conceptually with multiple fields there are multiple pointers tothe “first line” (at the end of blanking between each field) that arespaced differently but progressing at the same rate past each line. If acolor field is shorter, then the time between the time steps will beshorter, but the clocks between lines stays the same. What changesbetween fields that each field working on a different line of thedisplay at a given time, and optionally, the weighting of time betweentime steps for the various fields. Because the time between lines staysthe same, the pattern of the reads and Conditional setting and resettingremains the same.

For field sequential color with a rotating color wheel with all thecolor segments equal, it would simply be a matter of running the singlefield mode at the faster field/line rate by running the process at ahigher frequency.

With color Field Sequential the “line time” for the programming is thenumber of clocks it take the “spoke” to pass a given line. With arotating color wheel with multiple color segments, with the width of thecolor segments varying to create color fields of unequal time, the rateat which each spoke (change in color field) passes a given line on thedisplay is a constant set by the rotation of the color wheel. Becausethe time between line starts is a constant, the pattern of MRAM and ERAMcycles may be a constant thus simplifying the programming.

One straightforward method to program the color sequential fields ofunequal time duration would be to have at least a many program steps asthere are total fields times the number of ERAM reads per each field.While this would work and may be practical in some cases, it would meanrequiring a higher clock rate than would otherwise be necessary. Becausethe fields occur sequentially it would be possible to reduce the numberof program steps between lines and thus reduce the clock rate of theprogram.

In color Field Sequential with the raster processing the processing isscheduled to spread out the processing of the various lines and thevarious count steps for the various weighting of time don't all startand stop at the same time. The later time steps of the later lines willoften overlap in time with the time steps in the beginning lines in thenext field. With some display technologies such as LCoS, there will be a“blanking time” between fields that would allow at least some of thetime steps, particularly the LS Time steps and the lower ordered MS TimeSteps to be completed before the next field begins. What is key is thatthe time slot is no longer needed by the previous field before the nextfield “reuses” it. In effect a ERAM read or MRAM update cycle may beprogrammed to two or more different fields to occur at the same time,and other hardware selects between the which operation is performedbased on which field will be active at that point in time. By sharingtime slots, the number of clock cycles and program or other controlstorage may be reduced.

In the previous discussion, the assumption is that the various bitsstored in the memory represent the actual pixel bit value that willcontrol the mirrors. It will be noted that the deductive compare processsimply logically ORs selected bits together. A logical OR is acommutative process and the order of operations has no effect on theresult. In order to save on-backplane memory, it may be desirable forgiven periods of time to logically OR together one or more MS-Bits andsend the result, known as a summary bits of this OR of some or all ofthe MS bits to one or more ERAM buffers (for example, circular buffers)on the backplane. The panel processing would simply OR (or whateverother operation it would have done) this Summary bit instead of needingto OR in one or more MS bits.

With the dual count and deductive compare methods, the MS bits need tobe stored the longest and thus need the most storage on the backplane.In some embodiments of the present invention, it will be desirable toreduce the memory on the backplane. This method reduces the storage byhaving the panel interface controller (PIF) if there is an externalcontroller or by the backplane itself if it is directly connected toexternal memory store data.

The deductive compare method does a logical OR of selected bits of thepixel's value and that a logical OR is commutative in that the resultdoes not depend on the order of operations. It should also be noted thatthe MS-bits change at a slower rate than the LS-bits in a compare to acount type of process.

An example with a 10 bit count process, either single field, scrollingcolor, or field sequential with a dual count method split 5-MS and 5-LSbits is described below assuming no blanking time (blanking time reducesthe storage need as more lines are not needing any bits). Assumingbinary time weighting, each the 5-LS bits will require storage for lessthan 1/32^(nd) of the time using the deductive counting methods or about4/32^(nds) of a bit for all 5 bits assuming reallocation as each bitfrees up. The 5 MS bits taken together require about 4 bits of storageassuming reallocation of the bits.

FIG. 25 is a table providing an example of how summary bits areproduced. The 4 Most Significant bits, the 4 MS bits numbered 9 to 5will be kept off the backplane in external memory. These bits will beread and then “summarized” into a single bit that would be in thisexample, the logical OR of whichever bits are needed by the deductivecount method. The MS compare process is thus be broken into 16 groups bycorresponding to the 4 MS bit values (0 to 15). This summary bit wouldthen be ORs with the one MS-bit (bit 5) that is stored in a buffer onthe display.

In the deductive compare method using recursive feedback for the MSbits, the only bits that are looked at are those that would are a zeroin the current compare value. This means that for the count compare casewere all 4 MS bits are one in the 4 MS bits stored off the display,there will be no need to send or save the MS summary bit. Thus thestorage for the summary bits in the ERAM is roughly 15/16^(th) of a bitor less if there is blanking time factored in. Also it is only necessaryto send the summary bit 15 times per field (and not 16).

The summary bit process while reducing storage increases the bandwidthto the panel device. In the example of 4 MS bits being saved off thedisplay, instead of sending 4 bits once at the beginning, 15 summarybits will be sent when needed. Thus for a 10-bit pixel value process,instead of sending 10 bits to the device, 6+15=21 bits are sent orslightly over double the total bandwidth is required. This process ofsummarizing the 4 MS bits, however, can save up to about 2.5 bits ofERAM storage per mirror on the display device.

In a split counting and deductive compare process with 5 MS bits,without the summary bit, there would need to be initially 5 bits storedin the ERAM per mirror as the MS processing starts. There would be 32steps (2**5=32). With the 4 MS bits of the 5MS bits stored off thedisplay, there would initially only are 2 bits, 1 Summary bit and the 1least significant of the 5 MS bits. On the zero'th step, the summary bitwould be a 0 if all 4 MS bits are zero or a 1 if any of the bits is a 1.This summary bit would OR with the 1 least significant bit of the 4MSbits to decide on the control of the mirror, to reset if all the bitsare 0.

On the next step (“count”=1) the same summary bit would be used and theleast significant bit of the 5 MS bits that is saved on the displaywould not be looked at. As soon as the summary bit is looked used, inthis step, it is not needed again. It will be understood by thoseskilled in the art, that the MS processing is happening at a much lowerrate than LS processing, so there will be time to either bring in andoverwrite this location before it is needed for the next step, or usingcircular buffering methods the processor may wait until more near thetime the Summary bit is next needed and on average reduce the totalstorage needed for the summary bit by about half, since the bit wouldonly need to be on the backplane from the start of the even state untilthe start of the odd state.

On the next step (“count”=1) the same summary bit would be used and theleast significant bit of the 5 MS bits that is saved on the displaywould not be looked at. As soon as the summary bit is looked used, inthis step, it is not needed again. It will be understood by thoseskilled in the art, that the MS processing is happening at a much lowerrate than LS processing, so there will be time to either bring in andoverwrite this location before it is needed for the next step, or usingcircular buffering methods the processor may wait until more near thetime the Summary bit is next needed and on average reduce the totalstorage needed for the summary bit by about half, since the bit wouldonly need to be on the backplane from the start of the even state untilthe start of the odd state.

In typical signal processing the entries in a circular buffer are datasamples representing a value. In the case of one embodiment of thepresent invention an “entry” in the circular buffer will be one bit ofthe pixel value for a whole line of pixels. Thus a single “entry” in thecircular buffer is in bits the width of the mirror array but only 1 bit“deep”. This is in contrast to the common use of circular buffers wherethere is generally 1 entry of n-bits “deep.” For example, a 1920×1080mirror display with the memory rows going in the long direction, therewill be 1920 bits in one entry of the circular buffer.

Circular buffering is one of many methods for reallocating memory in arelatively continuous process and is used in one embodiment of thepresent invention. Methods of reallocation of memory other than circularbuffers may be used that would still use other aspects of the presentinvention.

Generally, a simple circular buffer requires the following information,however it will be understood by those skilled in the art that thevarious values may be “factored” or computed in various ways:

1. A pointer to the to the current writing location2. A pointer to the current reading location3. A start of buffer addressi. An end of buffer address

A more detailed description of a circular buffer is provided below withrespect to FIG. 95.

Often as is the case, and in one embodiment of the present invention,circular buffers are written to/filled by one process, and are then readfrom by a separate process. The write and read processes have to becoordinated to proceed at the same overall rate and the buffer is largeenough to allow for the read process to be safely behind the writeprocess and the write process cannot overwrite data before the data isfinished being used or is moved somewhere else. The length of thebuffers for each bit position can vary according to the length of timethe bits are stored on the device. Bit positions that “live longer” willrequire larger (longer) circular buffers. Thus as a minimum, the bufferwill generally be long enough hold all the bits that are “live” plussome amount of extra buffer space (buffer slack) to allow for somevariability between by either the read and write processes to thecircular buffer.

Sometimes the numbers controlling the pointers to the circular bufferare factored in different ways, such as having the pointer index off ofthe start of buffer address. The end of buffer address may be given bythe start of buffer address plus the length of the buffer. Some circularbuffering methods put power of two or other boundary restrictions thestart of buffer address and/or the end of buffer address and/or thebuffer length, and as a group any restrictions on a length or addresslocation will be call granularity restrictions. Granularity restrictionsoften result in needing extra memory to meet the restriction, and areavoided by methods of one embodiment of the present invention in orderto reduce the memory requirements.

The addressing of memory in such a way as to create a circular bufferwill be referred to as circular addressing. It is the control of theread and write addressing that in effect turns a linear memory into acircular buffer.

Circular addressing is often supported in Digital Signal Processor (DSP)in hardware. In the common use there are only a few circular bufferssupported (usually 8 or less). The circular buffers are treated as anaddressing mode of the processor and the number of circular buffers islimited both due to the cost of supporting circular buffering and by theneeds of the DSP applications. In contrast, in one embodiment of thepresent invention there may be a large number of circular buffers beingmanaged (in some embodiments it may be hundreds of buffers). Thus anefficient method of managing the buffers is required.

In a typical programmable processor such as a digital signal processorsthat are well known for supporting circular buffer in their addressing,when using circular buffers, the instruction points to address registersand index registers and often have other registers that control thecircular buffering that are either pointed to separately or are impliedby the registers that are being used. There is thus a series of pointersto other pointers. This indexing process to access the pointer and thecircular buffer control registers may become cumbersome as the number ofcircular buffers becomes large. In one embodiment of the presentinvention, the program and associated circular buffer pointers andbuffer control values will be kept in a “flat” structure whereby eachinstruction has associated with it the pointer into the circular buffer,the start of buffer value, and the end of buffer value. While there issome redundant information inherent in the flat data structure itgreatly simplifies the overall control processes and the controlhardware while at the same time being more flexible in some aspects.

In a simple circular buffer, a given data value is written once data andoften only read once. In the case of one embodiment of the presentinvention, the bit values are read multiple times and multiple differentpoints in the same circular buffer will be accessed contemporaneously.

In one embodiment of the present invention, keep multiple read pointersare kept, one read pointer for each time a data value is to be read fora given comparison. Also in one embodiment of the present invention, theindexing will be “flattened/removed” so that each instruction hasassociated with it the pointers and the circular buffer control values.Flattening the indexing will result in more memory bits being requiredbut will simplify the hardware and support more flexible control,particularly considering the requirement to track multiple values in thesame circular buffer and making multiple accesses into the same circularbuffer contemporaneously.

It should be understood that that alternative implementations of thepresent invention may employ indexing to reduce the amount of memorynecessary to store the circular buffer pointers and control registers.

Backplane controller buffer read and MRAM write control will bediscussed below. In one embodiment of the present invention, the bufferwrite (filling) and buffer read processes along with its associatedprocessing and MRAM write process are implemented largely separatelywith some synchronization.

In one flat instruction control embodiment of the present invention,each instruction has a “fixed” instruction in the Program control RAM(PCRAM) and a location in a “variable” control ram (VCRAM). It will beunderstood that some level of indexing may also be used to save on someof the control memory.

The circular buffers are filled by a separate control process. Thiscontrol process may be external to the device in a panel interface (PIF)controller. The PIF or the backplane itself may control data sent intothe backplane for the buffers and specify where in the buffer that theygo. The write process does what is necessary to add data to the buffer.The write process may be controlled by the same controller as the readprocess and use the same instruction field or more commonly, it may bemore loosely tied with some form of synchronization signals to keep theread and write processing sufficiently synchronized so that the circularbuffers are have the data available when needed without overwriting datatoo early.

For the rest of the description below of the read process control, thewrite or buffer fill process will be assume to be doing whatever isnecessary to keep the right data in the circular buffers

As has been discussed above with respect to panel control timing of thepresent invention, the panel effectively has an “inner loop” of thecontrol sequencing or patterns that is determined by the “time betweenline starts.” With a 3-color scrolling display, there are conceptually 3lines starting every so many cycles as the color scrolls across thedisplay. Note a Red, Green, and Blue line all “start” at the same timebut were they start on the display may not be uniform (for example, ifRed is longer than Blue or Green). For the case of the 540 fields persecond display there are 3 fields starting 180 times a second.

With a 1080 line display and 5% overscan (scrolling image opticallyextends beyond the display as it raps around from right to left or leftto right) there will be 1080×1.05=1134 line starts. The line start rateis 180 (fields per second)×1134 (lines/field)=204,120 lines per second.Assuming a 10-bit dual count split 5MS and 5LS bits there will be about160 ERAM bit line reads per each field and with 3 Colors there will thusbe about 160×3=480 ERAM reads per field. If we assume a split ERAM sothat 2 ERAM accesses may be made per cycle, then there will need to be aminimum of 480/2=240 cycles per line. To give some leeway for schedulingon the order of 300 cycles per line would be desirable. Thus the programmemory should be on the order of 300 instructions long. Multiplying the204,120 lines per second by the 300 cycles per line provides a clockfrequency for the processing of about 61 Million instructions persecond.

To give some leeway for different clock rates and other variables, theProgram RAM length might be rounded to 320 states.

In a traditional stored program processor, the inner and outer loopcontrol would be handled by instructions. In a traditional hardwiredcontroller a series of counters, decoders, and other hardware controleverything. In the processor of one embodiment of the present invention,there may be effectively only and “inner loop” that repeatsindefinitely.

The “outer loops” of operation are kept track of by the Variable controlRAM (VCRAM). This RAM is essentially a series of pointers into eitherERAM data Queues or to write Pointers to the Display mirrors. The“State” of the Panel Device is the combination of the Address Counterthat sequences the PCRAM and the whole contents of the VCRAM. Thecontroller supports the entire state of the controller being loadedwhile continuing to operate.

FIG. 26 illustrates a BCP (backplane control processor) 2602 of thepresent invention, including an address counter 2606 that is used togenerate addresses that sequence the instructions in PCP 2602. In theembodiment of FIG. 26, address counter 2606 is a simple counter thatwhen the count reaches predetermined value held in CA_end register 2608is reset to its start value. A CA_Reset signal 2610 may be used to forceCA_Counter 2606 to a known value, for example, to make sure thebackplane is in Sync with data input. A current counter value is outputon address lines 2612 and goes to various RAMs and/or ROMs including theTest ROM 2613.

A program CRAM, PCRAM 2614, generally contains the instructions andparameters that don't change with each complete cycle of the programloop. An update signal 2616 connects to a write input 2618 of PCRAM2614.

The program CRAM in one embodiment reads except when it is beingloaded/updated with the instructions. One of the features of thisembodiment is the support for writing to the PCRAM while instructionscontinue to be executed. In a display application, in normal use signalsmay become interrupted by, for example, a user plugging and unpluggingcables. A feature of the embodiment of FIG. 26 is support for thereloading of the instructions at a periodic or other rate in case thereis some loss of synchronization. The data output of the PCRAM are theinstructions that control the backplane. There will be various fields inthe instructions for controlling various functions of the backplane.These fields may be 1 or more bits wide as necessary.

Control signals for test 2620 which may either be enabled by some teststate of the machine or may be downloaded to the PCRAM as part of a testprocedure. A PE Function Code field 2622 is used to tell one or morearrays of processing elements (or PEs which are not shown in FIG. 26)what function to perform.

In the case of controlling two or more linear array of PEs there may bedifferent PE signals for each of the PE arrays so that they may performdifferent functions. These function control signals may include signalsthat control functions related to the PEs including the DATA value(s)that are written to the MRAM, signals that control anyregisters/latches/buffers associated with the PEs, and whether theoutput(s) of the PE are to be used to control the MRAMwrites/conditional writes (setting/resetting of the MRAM). It is alsoanticipated that in other embodiments that the PEs may be used tocompute values that are written to the ERAM.

ERAM write slot signal(s) 2624 are used to indicate when a given ERAM isnot being needed for a READ operation. If there is more than onephysical ERAM may be more than one ERAM write slot signal. If thissignal is active, the address pointers pointer generated by data pathsone or both of data paths 2626 or 2628 may be ignored.

The primary purpose of the ERAM write slot signal(s) is to communicateto other logic on the backplane when it is permissible to update/writeto the ERAM with new data (for example, the write process of thecircular buffering embodiment). There should be enough of these writeslot times to support the write process without there being a loss ofdata. In one embodiment, it is assumed that incoming data will be storedin the incoming shift registers to wait for one of the write slotsignal(s) to select the write address and data (from, for example, aserial-in/parallel-out shift register) for a circular buffer writeprocess.

In the embodiment of FIG. 26, MRAM write output(s) 2630 which areenabled versions of the Program CRAM output 2631 gives a broadcastedwrite enable to the MRAM (in the embodiment shown, there is only oneMRAM array being controlled by a single data path). The program CRAM2614 has Upper ERAM Buffer Start (BSU) 2633 and End (BEU) 2632 multi-bitoutputs. An end of display value in register 2634 and MRAM address 2636go to a comparator 2638 and if the MRAM address 2636 is beyond thedisplay, display write output 2630 will be inhibited by AND gate 2640.This comparison and gating of the Display write is one way to supportover-scanning.

The MRAM WE signal in some embodiments enables the bit masked write tothe MRAM.

FIG. 26 shows a Low ERAM previous buffer pointer address coming out ofmultiplexer 2642 which is compared against the end of buffer for thelower ERAM (BEL) in greater than or equal to comparator 2644. If thepointer is greater than or equal to the BEL, the multiplexer 2646 iscontrolled by a select signal 2648 so as to output the Buffer StartAddress for the Lower ERAM (BSL) as the Lower ERAM address 2650. Asimilar set of hardware inside data path 2628 may be used to compute canthe Upper ERAM address 2652 using end of buffer for the lower ERAM (BEL)and the Buffer Start Address for the Upper ERAM (BSU) signals.

A least significant bit 2658 of counter address lines 2612 goes to thewrite input of the VCRAM. The rest of the address bits 2660 are shiftedright one and used either immediately via multiplexer 2661 or aredelayed by a series of latches 2662 by the amount of time necessary tocompute the updated values for writing back to the same addresses on alater odd address counter state through multiplexer 2661. The output ofVCRAM address multiplexer 2661 is used as an address 2665 into theVCRAM. In this way on the even cycles, bits are read and on odd cycles,bits are written.

FIG. 26 shows data paths 2626, 2628 and 2666 for computing the addresspointers based on a combination of PCRAM 2614 and VCRAM 2667 signals andother data/control storage. Also, there may be nearly identical sets ofhardware that control the various pointers. Part of a data path 2626 forthe “Lower ERAM address” will be described below in some detail.

Even cycle address pointer 2668 and odd cycle address pointer 2670 forthe Lower ERAM Address (EPL) are fetched at the same time. The latch2671 is updated on every other cycle with the odd value 2670 to hold itfor an extra cycle. Multiplexer 2642 is used to select between evenvalue 2668 on one cycle and odd value 2670 on the next cycle undercontrol of the LS Address counter bit 2658. Not shown, but used for the“test and update” operation of the controller would be the option to putthe output of a multiplexer 2672 in the high impedance state if the Testor Update functions are used to support the “wired multiplexer” 2673.

Comparator 2644 checks if the pointer less than the corresponding BEL,buffer end value 2674. If the pointer is equal or greater than bufferend value 2674, then the comparator 2644 outputs a select signal on line2648 which goes to the select line input on multiplexer 2646 to select abuffer start value 2675 or previous value 2676 after being incrementedby an incrementor 2677. The output of multiplexer 2646 is a next LowerERAM address 2650.

A latch 2679 is controlled by a signal, least significant bit 2658, tosave the result, next Lower ERAM address 2650, of the odd locations onevery other cycle. A buffer 2680 is used to isolate the output, lowerERAM address 2650 from the ERAM data coming out on read cycles or todrive the new value in on write cycles. On write cycles, buffer 2680 andlatch 2679 provide the two updated pointer values.

The Upper ERAM address and MRAM addresses are similarly computed usingdata paths 2626 and 2628, respectively. The Upper ERAM data path takethe BEU 2632 and BSU 2631 outputs of PCRAM 2614 to set the limits on thebuffer range. One difference in the MRAM address control path beginningand ending of MRAM values stored in latches 2682 and 2683, respectively,connected to the MRAM address control path by respective data lines 2684and 2685, whereas the Upper and Lower ERAM have a separate beginning andending buffer limits provided by the Instruction memory on each accessof a pointer.

FIG. 26 shows one of many possible embodiments for the Variable CRAM(VCRAM). In this embodiment a single ported RAM is used to store thevariable bits. An alternative embodiment would be to use a dual portedRAM. In the embodiment shown, the memory reads and writes on every otheraddress cycle from the control address counter. The LS bit of thecontrol address is split off from the rest of the control address bitsand used as a control signal. It will be understood by those skilled inthe art that this signal may be combined with clocking signals and maybe inverted, buffered, or time delayed to cause the operation of thecircuitry shown.

In the example of FIG. 26, the start value of program address counter2606 may be assumed to be zero but it may be another value that isstored in a register. While a simple counter method is shown, it shouldbe understood that a generation of a sequence of instruction addressesmay be performed by other means such as are found on commonmicroprocessors.

Also the address counter of FIG. 26 is effectively a program counter ofa stored program computer and the control and sequencing of this countermay be extended to do more complex instruction control includingoperations such a conditional branches as are found on stored programcomputers. The instruction address sequencing may be performed in otherways as are common to stored program computers.

For each read cycle, the bits for controlling two cycles are read andfor each write cycle, the bits for two cycles are written. This dualread and dual write process allows a single ported RAM to be used whilemaintaining an average of one read and one write per cycle. This is onlyone of many ways of obtaining this capability.

While there may be other variables contained in the VCRAM, a majorfunction of the VCRAM is to hold the address pointer(s) into the MRAMand the ERAM(s).

FIG. 26 shows one way to implement a control processor, according to oneembodiment of the present invention, that supports up to two ERAM readsand up to one MRAM writes. In other implementations there may be one ormore than two ERAM reads and any number of MRAM writes supported. Thetwo ERAM addresses are labeled “Lower” and “Upper” implying that theROWs of memory go in the horizontal direction of the display. Inalternative embodiments, the ROWs of memory may run in the display'svertical direction so that the ERAM would be left and right.

It should be understood that FIG. 26 is only a figurative representationof the control and latching. In actual practice, there will beadditional buffering of signals and data as will be understood by thoseskilled in the art.

FIG. 26 shows physically Separate PCRAM and VCRAM arrays, but it will beunderstood by those skilled in the art that this is only one of manyways to accomplish the same or similar functionality.

FIG. 26 shows an architecture for a panel with one MRAM array and twoERAM arrays of one embodiment, but it will be understood that theconcepts shown may be used to control any number of MRAM and ERAMarrays. This embodiment shows a circular buffer control mechanism wherethere is no indexing mechanism between the program instructions and thepointers so that there are one or more pointer values directlyassociated with each instruction. It will be understood by those skilledin the art, that an alternative implementation would be to have an indexvalue (often called “register number”) in each instruction that pointsto one or more pointers.

In the embodiment shown in FIG. 26, the pointers are simply incrementedby one each time. It will be understood that the pointers may beadjusted by values other than one. It should also be understood thatthis is just one of many ways to generate and control a series ofcircular buffers. It should also be understood that while the addressesmay increment by one each time that the physical location or decodes maybe such that the rows of memory may be physically separate.

The reason for reading pairs of values (in this case addresses) is tosupport an average of one read plus one write cycle on every cycle witha single access per cycle to the memory. It would be possible to useother arrangements of hardware to achieve a similar result such as adual access memory or accessing the VCRAM at twice the rate. The doubleaccess with alternating read and write approach would not generally workwell with an “indexed” method of accessing pointers, since thismechanism relies on the pointers for sequential instructions to belocated sequentially in the VCRAM.

An alternative single access per cycle VCRAM implementation would be tohave two VCRAMs, one of which would be read on every other cycle and oneof which would be written on other cycle wherein the pair of VCRAMswould read on alternate cycles. This approach may also support indexedaccess to the pointers providing that pointers are restricted to beingused on odd or even instructions or in cases where this is not possible,that some pointers are duplicated.

It will be understood by those skilled in the art, that there are manyways to support on average a read plus a write cycle in a single cycleboth with single ported memories and multi-ported memories.

Also shown in FIG. 26 is a Test ROM 2613 structure. This ROM may be usedto effectively force its values to be the control signals. As is commonwhen connecting multiple memories to a common bus, there is effectivelya wire'ed OR Multiplexer 2673. With a bus structure acting as amultiplexer, generally only one of the available inputs to the bus isenabled at one time, while the other inputs to the bus are disabled (aregenerally in a high impedance state). In addition to test, it ispossible that there may be one or more ROMs used to store fixed programsand initial values to load into the VCRAM or other Pointer Storagestructure. A test signal 2686 enables the output of the Test ROM whileat the same time disables PCRAMs outputs via its disable input 2687.Test signal 2686 may also disable (high impedance) the outputs ofmultiplexer 2642 through OR gate 2688 which controls the Multiplexerdisable signal 2689.

It should be understood by those skilled in art that there may be othersignals including timing delays of the test signal to affect the properoperation of the circuits involved. While in this example the Test ROMdrives all the signals, in alternative embodiments, the Test ROM mayonly control some of the signals with the PCRAM and VCRAM driving othersignals with selective disables of various data outputs.

An advantage of having a Test ROM on the device is that it can supportsome forms of test with minimal control or signaling and thus notrequiring extensive external test hardware. This may be particularlyuseful in early stages of device testing.

An alternative test method to using a dedicated ROM would be to load thePCRAM and VCRAM with a test pattern that has a test procedure in it.Once loaded the device would then go through a procedure that wouldeither self-test or work in conjunction with an external testing system.

An “on the fly” loading of the program and variable RAM supports loadingthe contents of the RAMs while still generating valid control signals tothe rest of the device.

Also shown in FIG. 26 is a method for “on the fly” loading of theProgram RAM and/or Variable RAM. In a visual display system it is commonfor the video display signals to be interrupted temporarily such as whenchannels are changed or in the case of an external display monitor ifthe video cables are unplugged and then re-plugged. This interruption ofsignal may cause the display device either get out of synchronizationand/or to loose parts of its control memory. In a totally hardwiredsystem of an alternative embodiment of the control, one or moresynchronization signals would get the control back in synchronizationwith the source data, but in the case of this embodiment with an all orpartially RAM program and variable RAM system, a single signal would notget everything in the proper state (set the data in the RAM to thestarting condition). In a typical programmable system, the device isstopped while program and initial data values are loaded, but this maycause problem in a video system.

The on the fly loading of the Program RAM is accomplished in theembodiment of FIG. 26 by sending the update data out as the signalswhile and writing the data, perhaps after going through other hardwarein the system, back into the PCRAM and VCRAM. If the system is insynchronization and the data being output is correct, then the updatingshould produce the same results on the address and control signaloutputs as would occur without the updating process and thus theupdating may be done “transparently” as often as necessary withoutcausing any change in the visual effect. If the PCRAM and VCRAM has beencorrupted or has gotten out of sync, or perhaps the display parametershave changed necessitating an update of either or both the PCRAM andVCRAM, then the updated values are written.

The update process would generally start by writing to some or all ofthe registers on a device including the CA end register 2608, llastlatch 2683, lfirst latch 2682 and e_disp register 2634, shown in FIG.26. The CA_Address counter, CA reset signal 2610, is then reset to aknown count, generally either zero or to, for example, a registerspecified start value (not shown) by reset signal 2610.

An update RAM 2690 contents may be loaded by the memory write signal,test signal 2686, going to the write input control 2691 and update data2692. When being updated, address input 2693 for the Update RAM 2694 isselected by the write signal, test signal 2686, to be the Update Address2694 provided by update logic. Some form of control and data bufferingwould send data to the backplane for the update process and subsequentlybe sent to Update RAM 2694. For example the update data may be send inspare time period where there is no need to send the pixel data.

Update signal 2616 causes the PCRAM 2614 to be written rather than beingread. This write mode causes the data lines of PCRAM 2614 to go to be inan input (write) mode. The update signal 2616 through OR gate 2688 andsignal 2689 also disables the outputs of the multiplexer 2642 in datapaths 2626, 2628 and 2666. With the PCRAM 2614 being written to andmultiplexer 2642 disabled, the update signal turns buffer 2695 which isnormally disabled to turn on and drive some or all of the lines in wiredmultiplexer 2673. In this way, the update RAM 2690 values can substituteits values for those that would come from the PCRAM 2614 and VCRAM 2667.

When the update signal 2615 is active, W_Update signal, test signal2686, will be inactive thereby causing multiplexer 2696 to send some orall of the C_Address Counter's output, address lines 2612, to be used asaddress input 2693 to Update RAM 2694.

It will be understood by those skilled in the art that by only usingsome of the bits (or a logical or arithmetic combination of the bits) ofthe address output that a partial update of the PCRAM and VCRAM may beaccomplished. This would allow the update RAM to have fewer addresslocations than the PCRAM or VCRAM. In the case of a partial update, theupdate signal would only be active during the time that the C-Addresscount would be at the points in count were the update is to occur.

In some embodiments the controller may make no distinction about colorsin hardware and may no color specific control signals even in the caseof a sequential color application. It simply executes a program storedin it PCRAM and VCRAM.

The backplane that is the subject of the present invention may beprogrammed to handle time bases other than binary weighting as wasdiscussed above in reference to FIGS. 18, 19, 20, and 21. It is alsopossible to change the time base from between various fields of the sameor different colors or to have different time bases for differentlocations on the display of the same field.

With the dual pulse method as shown in FIG. 10 and in other methodsthere is a tendency to have a phase jitter on certain transitions wherea step of a binary value of causes pulses that have a small differencein time weighting to have a significant difference in phase. In somelight modulating technologies, this phase difference may be undesirable.The following will discuss how the backplane can use its ability toflexibly use different time bases to reduce the average phase jitter.

In some embodiments of the invention, there will be lookup tables thatmap input pixel values into output pixel values that are used by thebackplane to generate the pulses. If a time base is changed in the waythe backplane is programmed, the entries in the lookup tables may bechanged to give almost the same pulse widths after the output pixelvalues are used with the different time base. Or in other words, byusing a different time base, input pixel values will be mapped intodifferent output pixel values. As will be discussed below, by using twoor more time bases and two or more sets of input pixel to output pixelmapping, the average worse case phase jitter for the pulse waveformsbetween steps of 1-bit in the input pixel value may be reduced. Theissues with phase difference is well known to be a problem in the caseof a smoothly shaded object with some light modulating technologies suchas some LCoS technologies. This technique may be most effective thefield rate is higher than the rate at which the image data changes.

The table of FIG. 27 is a simplified example of a method to change thetime base between fields and/or between display elements of the samefield to break up transitions that cause the worst case “out of phase”lateral fields in a smoothly ramping (stepping by 1) image. FIG. 28 iscompares how a pulse of input values 16 and 15 would map into timeweighted pulse using time base 1 and time base 2 of FIG. 24.

In the digital backplane of the present invention, the “time base” forcontrolling the pulse widths in some embodiments is fully programmableand adds no complication to the design. The time base between any LS bitstep or MS bit step does not have to be binary weighted but are insteadcontrolled by the “order of operations” as was discussed above withrespect to FIGS. 18, 19, 20, and 21, and have little or no affect thespeed of operation. Supporting more than one time base at the same timeadds only a little to the control logic and memory (which is a verysmall part of the total device).

The example given in the table of FIG. 27 is for a small/simple case of5-bit total count split into 3-LS and 2-MS bits. In a real system withgamma correction there will be more output bits than the input bits, butto keep the example simple, gamma correction is not shown. Note that the“gamma correction,” correction for the LC response, and the correctionfor the change in the time base (of this method) may be factoredtogether into a single “gamma correction” operation per pixel input, butthere would need to be two different correction tables based on whichtime based is used for a given field.

For this example, the first time base is assumed to be simply binaryweighted into 32 equal intervals (0 to 31) as shown on the left handside of the table. Thus the MS bits are “weighted” to be 8 times (23)the LS bit time for the first time base.

The second time base shown in the far right two columns is “distorted”slightly relative to the first time base. The LS-bits times are equallyweighted in this example (they may be other than binary weighted) butslightly longer. The MS bit weightings are not uniform and are picked tocontrol the transition points and to limit the difference in the timeweighting of the pulses with respect to the first time base. Using thesecond time base, there will be some “redundant mapping” of the 31 Inputvalues since this is an N to N mapping. This will not be an issue with asystem with gamma correction using a mapping from smaller to a largernumber of bits (for example, from 8 to 10 bits).

The “Time” shown in the columns in each time base are in terms offraction of one field's on time (a fraction between 0 and 1).

The MS and LS columns under the second time base show how the MS and LSbits would be mapped for the second time base. The time under the secondtime base shows the resultant time, and the “Delta” has columns thatshow the difference and the percentage error with respect to the firsttime base. The goal is to keep the “Delta” to about ½ of an LS-bit time(note this will be LS-bits AFTER the input is mapped up to more bits).

In a simple 3 LS and 2 MS split count case, the worst case phasedifference occurs between the LS bits=7 and the next MS-Bit value withthe LS-bits=0. In the Example below, for the first/binary time base,this worse case condition would happen between Inputs 7 and 8; 15 and16; and 23 and 24.

The second time base is slightly longer and thus changes on which countswhere the worst case transitions occur. For example the Transition fromInput=7 to Input=8 which is a worse case for the First time base, willmap to stepping only in the LS-bits in the Second time base (from MS=0and stepping from 5 to 6 in the LS-bits).

In the Second time base, the worst case phase error occurs between steps8 and 9, 16 and 17, and 24 and 25, which are all low phase differencecases for the First time base. Thus in a double field rate operation, ifthe different time bases are used for each field, the worst case phasedifference between two single steps will only occur in one of the twofields and thus the overall worst case effect should be roughly halved.

For the digital backplane of the present invention, time is controlledby simple program sequencing. The time between any LS step and/or any MSstep may be essentially any amount. Thus time may be “distorted” in anessentially infinite number of ways including ways that may be useful tocompensate for the LC response. The First Time Base may be also slightlydistorted from a simple binary weighting as well (for example, madeslightly shorter).

FIG. 28 shows graphically the phased difference between an input valueof 15 and an output value of 16 for the two time bases of FIG. 27.

Currently with spatial light modulators, compensation tables known as“gamma” tables are used to control the output pulse weighting using afixed time base. In some embodiments of the present invention, using anon-binary weighted time base may be used to obtain the benefits ofthese tables without the cost associated with lookup tables and perhapsmore importantly the usual increase in data from the input pixel tooutput pixel mapping. In addition to eliminating the cost of the tables,there is the issue that gamma tables generally map to more output bitsthan input bits. Thus the amount of data that has to be moved, stored,and processed after the mapping is increased. By manipulating the timebase in a non-binary weighted method, the benefits of a table lookup maybe achieved without requiring the physical lookup table. The ease withwhich some embodiments such as that of FIG. 26 may be programmed canfacilitate the use of time bases. In effect the programming can have the“gamma” (or other weighting table) programmed into it and thus eliminatethe need for mapping the input pixel values.

In some embodiments of the present invention, there may be a singlecount method (equivalent to the dual pulse method where all the bits aretreaded as MS Bits) employed for controlling the pulse while obtainingother benefits from other features of the present invention such as thereduction in data and bandwidth from deductive counts. With a singlecount pulse width control, it becomes relatively easy map input pixelvalues into any desired pulse width time weighting by the methodsdiscussed for FIGS. 18, 19, 20, and 21. With some embodiments wherethere is a RAM based program store such as with FIG. 26, the mappings ofinput pixel values to time weighted pulses may be as flexible or moreflexible than it would be for the table lookup approach.

In embodiments such as that of FIG. 26, extremely fine control of thetime base may be achieved such that what would require mappings of alarge number of output pixel values with the lookup table approach maybe achieved at little or no additional cost, particularly relative tothe cost of dealing with the additions bits of data after a remapping toinput pixel to output pixels with more bits in the output pixels. Ineffect the time based is remapped.

The previously mentioned U.S. Patent Application Document No.2003/0160803 to Willis (hereafter referred to as the '803 Application),the entire contents and disclosure of which is hereby incorporated byreference demonstrates in FIG. 10 several aspects of the prior art thatare solve by one or more embodiments of the hardware and methods of thepresent invention including the use of adjusting the time base ratherthan using table look-ups for weighting the time value of input pixelsjust described. The '803 Application, in FIG. 10, shows an m-bit counterdriving at 2^(m) by n-bit lookup table were n is usually greater than m.FIG. 10 of the '803 Application shows the need for storing n-bits forevery pixel in the in the display. By just using the time baseadjustment method of mapping just described only m-bits (where m is lessthan n) would need to be stored. Then by further improvements of thedeductive compare and using a “single count method” to generate thepulse with recursive feedback the same pulse waveform may be effectivelygenerated with significantly less than even m-bits per pixel.Furthermore, the deductive compare hardware and methods would reduce thenumber of bits of data that would be required to be fetched using thebit serial techniques taught by some embodiments of the presentinvention. As an example, for m=8 and n=12, there may be a reduction onthe order of 32× fewer bits to be accessed and processed combining thetime based mapping and deductive bit serial compares.

One of the issues that might otherwise occur with time base remapping,particularly if it is done in hardware, is the problem of scheduling allthe reads (for example, from ERAM) and writes (for example, to MRAM). Aswas discussed above with respect to FIGS. 18, 19, 20, and 21, and withan embodiment such as is shown in FIG. 26, the scheduling process of thepresent invention allows a high degree of flexibility in scheduling.

In some embodiments of a system with the present invention, the timebased remapping “program” may be pre-computed and saved in memory (ROMor RAM) either on the backplane or in memory external to the backplane.In other embodiments the time based remapping may be computed byhardware either on the backplane or off the backplane to support a widerange of remapping values, including those based on user controls.

The dual count approach may also time based remapping. With dual counts,time based remapping may be used to expand the range of intensities butthere may be large “gaps” in the intensity ranges unless there is someoverlap in the pulse widths possible with the LS and MS bit timecontrols. Some remapping of the input pixels by table lookups may beused to prevent large gaps in intensity when combined with the timebased remapping with using dual pulse.

In FIG. 7 there is a block called “DC balancing” and the following willdescribe some new and useful circuits for supporting the “DC balancing”in hardware that can also support level shifting. The circuits describedbelow will be used to drive an electrical signal on an electrode thatmay also act as a mirror function, thus this electrode is commonlycalled a “mirror.” Each mirror will use the charge on that mirror tocontrol LC material on top of it. Also in one embodiment of the presentinvention, there may be an N by M array of such mirrors and drivecircuits so as to form a two-dimensional array of picture elements knownas Pixels.

In LCoS, LC material will generally be sandwiched between asemiconductor device and a glass lid with a very thin coating of aconductor that is thin enough that most light will pass through it. Avoltage potential is applied to the coating on the glass and on eachindividual mirror will cause the optical characteristics of the LCmaterial over each mirror to change. Usually it is the way the LCmaterial changes the polarization of light that is affected, and byusing a combination of polarized light and optical surfaces that onlypass light of a given polarization the light intensity may becontrolled. More information displays of this type are given in U.S.Pat. No. 5,959,598 to McKnight and U.S. Pat. No. 6,005,558 to Hudson,the entire contents and disclosure of which are hereby included byreference.

With advances in semiconductor processes transistors are being madesmaller, but higher voltages may damage smaller transistors. In order tohandle higher voltages larger and often slower transistors may beintegrated on the same device. LC materials generally require highervoltages to provide the best voltage potential for their opticalswitching characteristics. In order to integrate more transistors ontothe display device while still providing the drive voltages required bythe LC material, it will be advantageous to have most of the circuitryusing smaller transistors, while only a portion of the transistorsoperate at the higher voltages. In order to accomplish this, there willhave to be some form of “level shifting” for the lower voltage logic todrive the higher voltage logic.

The paper “Level Shifting Interfaces for Low Voltage Logic” to K. JoeHass and David F. Cox gives an overview of some known level shiftingtechniques and the entire disclosure and contents of this article ishereby incorporated by reference. As the paper points out, levelshifting downward is relatively simple, but level shifting upward ismore difficult. The paper in its FIG. 6 shows a well-known method ofcross coupling two P-Channel pull up devices.

The circuits described below will incorporate both the level shiftingand the ability to selectable hold and/or invert the output.

Most LC material require a that they have an average over time DC driveof approximately zero volts. This requirement is well known to thoseskilled in the art and is referred to by various names including “DCBalancing” (which will be used in the remainder of this document), “DCRestoration”, and “Debiasing.” U.S. Pat. No. 5,959,598 to McKnight andU.S. Pat. No. 6,005,558 to Hudson discuss this requirement and theentire contents and disclosures of these patent are hereby incorporatedby reference.

U.S. Pat. No. 5,959,598 (hereafter the '598 patent) to McKnight shows an“XOR” gate driven by a “global signal” to invert the voltage on adisplay mirror. U.S. Pat. No. 6,005,558 (hereafter the '558 patent)“Display with multiplexed pixels” to Hudson et al shows an “multiplexer”that selectively connects one of two voltages to the a display mirror.U.S. Published Patent Application Document No. 20030038651 (hereafterthe '651 application) “Display device test procedure” to Zuravleff showsin FIG. 4 a transistor level implementation of a multiplexer (labeled 42in FIG. 4) driving a display mirror as described in the '558 patent.

The '598 patent shows an XOR gate with a global signal going to allnodes. An XOR gate can take a number of transistors to implement.Furthermore an XOR gate would not generally support changing the voltagelevel of the inputs to the outputs.

As discussed in the '558 patent and hereby incorporated by reference,due to the voltage drive requirements of the LC materials, it may bedesirable to have a different voltage on the mirrors than that whichdrives the rest of the circuitry. The '558 patent and the '651application describe level shifting, but in order to perform the DCBalancing function requires that the both of the voltages supplyterminals have their voltages changed. This means that a large amount ofcurrent will have to move through the device in order to accomplish theDC balance function, since not only will the voltage on the mirrorschange, but that voltages on all lines carrying the voltage supplies tothe mirrors have to move.

While the '558 patent says that analog multiplexer may support voltageshigher or lower than the selection signal on the multiplexer, thecircuitry to support it are not show.

Support for multiplexing a voltage higher than the gate voltagecontrolling the multiplexing is significantly more complex than for avoltage at or lower than the multiplexer's control voltage. The '651application, for example shows, an analog multiplexer, but it isquestionable how well the circuit would work if the voltages weresignificantly higher than the gate voltage on the P-Channel gates of themultiplexer. One of the objects of the present invention is to provide acircuit that can work with mirror voltages higher or lower than the restof the circuitry of the device.

Having a digital circuit that drives different voltage output levels iscommonly known as “level shifting. The inverting level shifter that isthe subject of the present invention accomplishes both a voltage levelshift as well as being able to selectively invert the voltage shiftedoutput. Furthermore, it has the advantage of accomplishing this withoutrequiring that the input voltage levels to the circuit be changed.

FIG. 29 is a diagram showing a bit cell with inverting level shifter inaccordance with an embodiment of the present invention. A minus “−” signwill be used to indicate logical False signal. Also for the purposes ofthis description, a voltage near 0 volts will be considered to be alogical 0 and a Voltage nearer one of the supply voltages will beconsidered a logical 1.

On the left side of FIG. 29 is a conventional 6 Transistor (6-T) staticRAM (SRAM) bit. There are two inverters (of two transistors each) thatare cross-coupled to each other to form a storage bit. There are two bitLines Labeled Bit and -Bit that serve to write and/or read bits as in atypical SRAM. Unlike a typical SRAM bit, the inverters are used to drivesome additional circuitry, namely transistors labeled T3, T4, T5, andTC. The transistors on the left side, particularly the two inverters maybe driven by a voltage that is less than Voltage that will be used todrive the mirror. For example the Vcc for the inverters might be 2.5Volts.

The two cross-coupled P-MOS transistors T1 and T2 act as the pull uppart of a level shifter to the higher voltage than that of theinverters, for example 3.3 Volts.

There are two control signals, CTrue and CFalse, that are used controlthe inversion function of the circuit. Nominally, these signals may bethe same voltage as that of the inverters.

If CTrue is on (logical 1) and CFalse is off (logical 0), then if A=1Node NnM will be pulled down via the transistor T5 and transistor Ttconnect to C-True. This will also cause the PMOS transistor connected toNM to turn on thus driving the mirror to the High Value, or 3.3 Volts inthis example. With C-False OFF, the node F2 will be driven by T6 toabout a Vtn below the Gate voltage on A through transistor T6.

If CTrue is once again on but A=0 so that -A=1, then -A will pull downnode NM through T4. This will in turn cause T1 to pull up node NnM. NodeF2 will then be pulled up to about a Vtn below the gate voltage on T3.Thus F2 will always be about a Vtn below the value of the Vcc of thelower/normal voltage of the bit cell driving the level shifter, IFFC-True is ON and C-False is OFF.

If CTrue is OFF and CFalse is ON and if A=1 then node NM will be pulleddown through T6 and Tf. With NM driven to 0, it will turn P-Channeltransistor T1 on thus pulling up node NnM. Node F1 will pulled up aboutone Vtn below the voltage on the gate of T4.

If CTrue is OFF and CFalse is ON and if A=0 so -A=1, then node NnM willbe pulled down via T3 and Tf. With T6 turned off by A=0 and node NnMpulled down to 0, the P-channel transistor T2 will pull node NM to the3.3 Volt high level. The Node F1 will follow node NM but will be lowerby about a Vtn of the gate voltage on T 4.

If both CTrue and CFalse are off then there is no path to ground for thelevel shifter. Given time the output on the nodes NnM or NM may driftupward if they were in a low state, but for a period of time nodes willremain in their state before both lines were driven off due to theself-loading of the circuit. This function of control lines CTrue andCFalse both being high, may be used to control when a change on nodes Aand -A will cause the mirror connected to node NM to change.

A requirement is that control lines C-False and C-True must not both beon at the same time or there will be a short circuit. But it is OK forthem both to be OFF at the same time and may provide added functionalitywhich may be useful during transitioning the output. For electricalreasons, particularly if the transition of signals CTrue and CFalse maybe slow, it may be preferred turn one off before the other is turned onto insure that there are no power surges.

FIG. 29 shows “explicit” control pull down transistors Tt and Tf. But itshould be noted that the nodes F1 and F2 either are driven to ground bytheir respective control lines or are driven to about a Vtn lower thanthe bit cell's Vtn. Thus these nodes may be shared between multiple bitcells OR just a line that is driven to ground or “floats” and is pulledup by multiple cells. Thus transistors Tt and Tf may be eliminated insome implementations as shown in FIG. 30. Note that -CTrue when drivento ground will have the same logical function as CTrue of FIG. 29 hadwhen driving Tt with a logic one. Similarly, -CFalse in FIG. 30 whendriven to ground will have the same function as CFalse had when drivingTf in FIG. 29 with a logical 1. When -CTrue is driven and -CFalse is“floating,”-CFalse will tend to be driven to about a Vtn down from theN-channel transistor gate voltage. There may be some driving circuitsexternal to the mirror that drive this node to about a Vtn down from Vccas well. -CTrue floats and -CFalse is driven to ground, -CTrue will tendto be driven to about a Vtn down from the N-channel transistor gatevoltage through transistors in the level shifting and inverting circuit.There may also be some driving circuits external to the mirror arraythat drive the control signal to about a Vtn down from Vcc as well.

It is well understood that it is important to be able to test as much ofthe circuitry of a device as possible. U.S. Pat. No. 6,650,138 showsadding additional circuitry to a display cell to just to support test.It is a further improvement of this invention that the circuitry can betested without additional special test circuitry within to the displaycell or extra control signals to the display cell as will be described.

One embodiment of the invention shown in FIG. 30 supports test withoutaddition circuitry on a per mirror/cell basis. The control lines -CTrueand -CFalse can be connected to say either one row or one column ofcells in the array. In FIG. 30 they are shown running perpendicular tothe bit lines and parallel to the select line, but they may instead runparallel to the bit lines.

In the test mode of operation, the logic level store on the SRAM bit atpoints A and -A can be used to effectively test both the level shiftinglogic and the SRAM bit itself. In one method of test, only one cell istested for every bit connected to a given -CTrue and -CFalse. There canbe multiple sets of the control lines -CTrue and -CFalse in the deviceso that multiple cells can be tested in parallel.

In test operation the fact that performing a series of operations andsensing Nodes F1 and F2 can be used to test the cell's functionality. Totest the cell may require a multiple step process, but since this isonly done for testing, it may preferable to adding special transistorsjust for test. An example procedure for testing both the level shifterand the an the memory bit is described below:

1. In the first step of the test process, all the bits sharing a commonset of control signals have their SRAM bit set to A=0 (and thus -A=1)with an SRAM write process via lines B and -B.2. Line -CFalse is driven low which will in turn drive node F2 low andif Transistor T3 is not open, it will put node NnM low through T3 whichin turn pulls NM high through T2. Note this will also cause line -CTrueconnect to node F1 to be pulled upward via transistors T3 on all thebits sharing this control line to a voltage level that is somethinglower than the Gate voltage on transistor T5.3. Line -CFalse is allowed to “float” and it is then checked withcircuitry external to the array of bits to see if it is pulled upwards,if it is pulled upward, then there is a short or open someplace in thein that group of bits sharing the control line and the device has failedthe test. And that fact will be noted by the test logic external to thebit array.4. Only the bit under test is set to A=1 while all other bits remain atA=0. Note control lines -CTrue and -CFalse are both floating. If thetransistors are acting properly in the bit, the line -CFalse will bepulled high via transistor T6. It will be noted that the mid level onnode F1 will go to node NnM that goes to the gate of T2. While this midlevel voltage will reduce the drive of T2, it should leave P-channeltransistor T2 sufficiently turned on and thus node F2 and -CFalse willbe pulled up. The result of these first steps verifies that the mirrorcan be driven to logical 1. It also tests the function operation ofmultiple transistors.5. Line -CFalse is first driven to zero and allowed to then float. If-CFalse is pulled up, then there is something wrong with the zerofunction of the Bit under test and it has failed and will be noted bythe test logic.6. All the bits connected to the -CFalse line are set to 1. The -CFalseline is driven low and then allowed to float. If the -CFalse line ispulled high, then there is problem in one of the bits and the test failsand that fact is noted by the test logic.7. Only the bit under test is set to a “0” and line -CFalse should bedriven up via T3 by the bit under test. As similar to in step 5 therewill be a “mid level” on the gate of T1. This test verifies being ableto pull down through T6, pulling up by T1, and that transistor T3 can beturned on. If line -CFalse is not pulled up, then there is a problemwith the bit under test and the test logic will not it.8. Next the set of steps 1 to 7 are performed but this time using line-CTrue to be driven and floated while line -CFalse remains floating.9. This test verifies being able to pull down through T6, pulling up byT1, and that Transistor T3 can be turned on.10. The procedure outlined above can be repeated for all the bitsconnecting to a set of control lines. Many bits can be tested inparallel if there are multiple sets of control lines. It is alsoanticipated that more than one bit on a set of control lines may betested at the same time rather than each bit individually as outlinedabove but it may require more elaborate circuitry to “sense” the stateof the control lines.

If at any time in the procedure outlined above an error is found, it maybe either saved in the test logic for later use or immediatelycommunicated for testing as is common in test procedures.

With the procedure outlined above or ones similar to it, thefunctionality of the transistors that drive the mirror can be verified.In fact a subset of the procedures outlined above may be sufficient togive a reasonable confidence as to the functionality of the circuitry.More combinations of bits being set and/or changed along with thedriving and/or un-driving of the control lines may be used to increasethe confidence of the testing.

It will be understood that there are many analogous procedures thatcombine setting SRAM bits and or changing SRAM while the control linesare either the driven or un-driven by the drivers outside the bits thatmay be used.

FIG. 31 shows that the concept may be extended to two or more inputlogical functions rather than simply inversion. FIG. 31 shows a circuitthat would support a fully general logical combination of two inputs Aand B (with their logical inversions -A and -B).

The control lines C1 through C4 are used to pull down node NnM and thencontrol lines C5 through C6 will be used to pull down node NM if thelogical compliment of the function that pulls down NnM is true.

Consider the simple case of putting a logical 1 on the node NnM; in thiscase C1=C2=C3=C4=1 and C5=C6=C7=C8=0. This will force node NnM downregardless of the state of A and B.

As another example, consider the case of putting logical A ANDNOT B onthe mirror. In this case, control line lines C3, C5, C6, and C8 will beon and the other control lines off. C3 will cause node NnM to be pulleddown in the case of A AND -B=1 and lines C5, C6, and C8 will pull downnode NM in all other cases.

The inversion operation one embodiment is supported by turning oncontrol signals C3, C4, C1, and C2 to output the logical value of A butat a higher voltage or C1, C2, C3, and C4 to output -A. In fact, thelogic of FIG. 29 may be seen as a reduction of the unnecessarytransistors and control lines from FIG. 31 when only supporting thefunction of A and -A are required.

It should be understood by one skilled in the art that the control lineswith a transistor pull down in FIG. 31 are only one way of implementingthe logic function and may also be reduced to nodes that either float orare driven to 0 as is shown in FIG. 30 for the simpler case of A and -A.

This concept may be extended to support the logical combination of morethan 2 inputs or to support a subset of logical combination other than Aand -A by one skilled in the art.

FIG. 32 shows a simple figurative example of a portion of a memory map3200 that has multiple circular buffers in it. Each circular buffer issimply a range of memory addresses that has memory address pointers thatare managed, often at least in part by hardware comparisons to one ormore limits, that when a memory access exceeds the end of the buffer theaddress will wrap around, modulo the size of the circular buffer, to thetop or start of the buffer. With the circular buffering method used bysome embodiments of this invention, the address pointer will only beincrementing by one address location at a time, which makes the circularbuffer address management process simpler since it can be controlled bysimply setting the address pointer to the start of a given buffer if thenext address will exceed the value for the end of the buffer. The sizeof the circular buffer is then simply the difference between the startaddress of the buffer and the end address of the buffer.

Shown in FIG. 32 shows a memory array 3202 with circular buffer 1 3204,a portion of memory that is unallocated 3206 for circular buffering andmay be used for some other use, circular buffer 2 3208, and circularbuffer 3 3210 in it. Only a portion of the memory 3202 is shown andthere may be more circular buffers and in some embodiments of thisinvention, there may be over 100 circular buffers in use at one time.Circular buffer 1 has a start of buffer address 3210 and an end ofbuffer address 3212, circular buffer. Circular buffer 2 has a start ofbuffer address 3214 and an end buffer address 3216. Circular buffer 3 isshown having a start of buffer address 3218 immediately followingcircular buffer 2's end of buffer address 3126 and has an end of bufferaddress 3220. The size and location of the circular buffers can be setindependently, but generally they will be set to not overlap. Thecircular buffers in some embodiments will be stored in one or moreERAMs.

It will be understood that the memory map shown is only figurative. Theactual physical memory locations for sequential addresses may be spreadout through the physical memory array. For a display device where someof this memory might be under display elements that may be affectedpower surges caused by the accesses to the memory, it may even befunctionally desirable to spread out the physical location of sequentialmemory addresses in order to spread to result in a more uniform powerrequirement across the array.

As is common with conventional uses of circular buffers, each circularbuffer may be filled by a write process that in one or more cycles fillseach entry of the circular buffer. The buffer needs to be long enough sothat the write process will not overwrite that same data before a readprocess has finished needing to access that data.

In some embodiments of the present invention, the circular buffers willbe “bit plane buffers.” The size of the various circular buffers requirein some embodiments will be related to how long a time certain bitpositions within a pixel or summary bits for a pixel are needed. In someembodiments access to the memory 3202 read or write as many bits asthere are light modulating elements in one direction of a spatial lightmodulator, but it will be understood that the concepts of this inventionmay be applied with more or less bits in one access. Having the circularbuffers be bit plane buffers has advantages for certain aspects ofvarious embodiments of this invention; specifically, it can lead toneeding fewer total bit accesses to do the processing necessary tocontrol the light modulating elements and because in some embodimentsthe length of time and thus the size of the buffer may vary by the bitposition within the pixels, it can lead to more efficient packing of thecircular buffers into available memory.

In one embodiment, the present invention provides an array of circuitsthat supports: voltage level shifting, a selectable logic functionbetween one or more input to generate the output, and using constantvoltage sources for the circuits. Such an array may be used to provide aviewable image on a visual display device.

The array of circuits may support level shifting higher than theincoming voltage and may be used to control the voltage on an electrodethat controls some output. The electrode may form a mirror or an arrayof mirrors of a display device.

The selectable logic function of the array of circuits may invert or notinvert the input and may perform a number of different logicalfunctions.

The array of circuits may use 2 or more cross-coupled P-channeltransistors to pull up the circuit to a logical high level such that oneP-channel device is fully off when the other device is fully on. Thearray of circuits may also include is a series N channel devicesconnected to each of the P-Channel devices. The purpose of theseN-channel devices is to optionally pull down one of the P-channel gatesand thus turn on exactly one of the cross-coupled P-channel devices. Ifthe Gate of the connected P-Channel device is not pulled down, then itmay be optionally pulled up and thus turned off by the other P-Channelgate.

The array of circuits may include two or more nodes that are eitherdriven or allowed to float and in which at most one node is driven atgiven time. The may be separate floating nodes in each circuit and thefloating nodes are shared between multiple circuits and wherein the actof driving the node or allowing it to float controls the local functionof the circuit. Common floating nodes of may be sensed in order todetermine the functionality of the circuitry.

The array of circuits may support inversion of the logical value storein a display cell that may be tested without adding additions dedicatedtest circuitry on a per cell basis.

In one embodiment, the present invention provides a visual displaydevice with an array of MRAM storage bits that are used to control anarray of electrodes wherein there are column drivers on both sides ofthe memory so that some or all of the rows of memory bits may be drivenfrom either side of the array. The storage bits may or may not beconnected to other circuitry in order to facilitate driving theelectrode. The visual display may be an LCoS, DLP™, OLED microdisplay orany other type of visual display.

In the visual display device, ERAM memory bits may be used to computethe values for driving the MRAM memory bits that go to computation logicon either side of the MRAM array. At least part of the ERAM memory bitsmay be inter-disposed with MRAM memory bits but where in the columns ofthe ERAM memory bits are such as to form two arrays where the sense ampsand buffers are on opposite sides of the memory array.

In one embodiment of the present invention, the present inventionprovides an array of storage bits used to control an array of electrodeswherein the array supports the operation of controlling the setting orclearing of selected bits rather than or in addition to the normalmemory operation of writing to a bit. The control of the setting orclearing of the memory bits may be with a masked write function. A dummyread is done on bits that are not set or cleared. Also, the bit itselfmay have separate set and clear inputs.

In one embodiment, the present invention uses bit serial processing tocompute the pulse width for an array of pulses. The pulses may used tocontrol the intensity of a visual display device. There may be one ormore sets of bit serial data processing elements and the one or moresets of bit serial processing elements may on one or both sides of oneor more MRAM type memory arrays. Each MRAM array may perform the sameoperation or different operations. The results of each operation may goto a MRAM driver on its corresponding side of the MRAM array. The MRAMmay support driving MRAM bits on only part of the array or on the entirearray.

The processing elements used in bit serial processing may compute thepulse widths using a sticky logical OR or a sticky logical AND or onlylogical operations and latch may be used to determine the pulse width ineach processing element. The processing elements may also compute thepulse widths using an arithmetic compare. Also only one subset of thebits corresponding to a pixel value may be used to determine the controlof a pulse width.

In one embodiment, the present invention provides a digital displaybackplane that can accept partially or fully encode partially encodedvalues for an array of electrodes using purely digital processing toconvert the encoded data to pulse widths by the backplane and whereinthe control of multiple electrodes is performed by programmable sharedcontrol with and multiple data path processing elements. Some of theprocessing involves operations on varying numbers of bit to be requiredfor each stage of the pulse width determination. Also, where a recursivefeedback method may employed. The recursive feedback method may employ:deductive comparisons, dual count method, and/or a bit serial operation.Memory addressing is used fetch fewer than all the bits of a pixel'svalue when making a determination of the next state of a pulse width.

FIG. 33 shows a backplane controller 3312 of a digital backplane 3314 ofa spatial light modulator 3316 of a visual display device 3318 inaccordance with one embodiment of the present invention. Backplanecontroller 3312 is part of a SIMD processor 3320, i.e., a bit serialprocessor, that also comprises arrays 3324 and 3326 of bit serialprocessing elements (PEs) and corresponding memory arrays 3328 and 3330or ERAM. Although, for illustration purposes, memory arrays 3328 and3330 are shown as being separated in two pieces, memory arrays 3328 and3330 may be physically in one or more pieces. For example, in theembodiment of the present invention memory array 3328 includes upperERAM 1712 and expansion RAM 1724 shown in FIG. 17, and memory array 3330includes expansion RAM 1725 and lower ERAM 1714 shown in FIG. 17. Arrays3324 and 3326 of bit serial processing elements are located on oppositesides of an array 3332 of light modulating elements of spatial lightmodulator 3316 and correspond to PEs 1736 and 1738 in FIG. 17. Array3332 comprises two (2) groups of light modulating elements, i.e., groups3334 and 3336 of light modulating elements. Array 3324 of bit serialprocessing elements uses bit serial processing to compute pulse widthsthat drive the light modulating elements of group 3334. Array 3326 ofbit serial processing elements uses bit serial processing to computepulse widths that drive the light modulating elements of group 3336.SIMD processor 3320, i.e., a bit serial processor, controls the lightmodulating elements of array 3332. In one embodiment, visual displaydevice 3318 may be an LCoS device.

In one embodiment, the present invention provides a display backplanewith an array of processing elements using bit sequential operations togeneral generate an output that controls a display element. Theprocessing elements may be capable of performing logical or arithmeticoperations on multiple bits with sequential operation to form a result.The accumulated operations result may be controllably inverted and oneor more results may latched for writing at a later time.

In one embodiment, the present invention provides a method forcontrolling an array of pulse widths that drive electrodes usingrecursive feedback of the current state of the output. The electrodesmay control picture elements of a display device and may be an array ofelectrodes in on a single silicon backplane. The recursive feedback mayexplicit such as with a separate feedback signal or with a memory readoperation. or the recursive feedback may be he recursive feedback isimplicit with a masked write operation or a set-reset type of storagefunction.

Not all of the bits that control the value of the pulse width are usedat each stage that determines the pulse width. An array of output pulsesmay be generated from binary values for an array of outputs where lessthan all the bits that determine the width of each pulse are used inmore than half the stages of the pulse width determination. At any givenstage only the bit locations corresponding to the zeros in the valueassociated with the current stage are used. Also, at any given stageonly the bit locations corresponding to the ones in the value associatedwith the current stage are used.

In one embodiment of the present invention, recursive feedback and bitserial processing may be combined to control an array of electrodes andthe array of electrodes may be used to controls the intensity of pictureelements of a visual display device.

In one embodiment, the present invention provides display process for avisual display device were the memory available on the display devicefor storing pixel values is reallocated and some bit positions of thepixel values requires less storage than other bit positions. Thereallocation method may be programmable. The data may be stored inqueues and the queues may be circular buffers. The number of storagebits required for each bit position in a pixel value varies based on thetime the given bit position needs to stay resident in memory for use bythe processing.

In one embodiment, the present invention provides a display process witha display device were multiple bit pixel values are stored on thedisplay device and where in storage location of the bit values may beprogrammed. The memory locations may not be dedicated to a given binaryweighting and thus memory locations may be allocated to different binaryweightings. Also, one or more of the buffers may be a different sizebased on the need to keep the data resident on the display device.

In one embodiment, the present invention provides a method forgenerating a single pulse by sending the pixel values in a binaryencoded form to a visual display device. The visual display devicetreats some of the bits as LS-group of bits and some of the bits MSgroup of bits and one of the group of bits in controls the time at whicha pulse starts and the other group of bits will control when the groupof bits stop and in so doing will create a single pulse. Once any of thebits are no longer needed for controlling their pulse width, the memorystoring those bits may be reallocated for storing other bits and such areallocation may result in less storage.

In one embodiment, the present invention provides a method forgenerating a single pulse on a visual display device by sending fullyencoded data values while requiring less storage on the visual displaydevice than 1 bit of storage required on the display device for everybit sent. There may be less than ½ bit of storage on the display devicefor every bit sent and recursive feedback may be used to control thepulses.

In one embodiment, the present invention provides a visual displaysystem were some of the bits values of the pixel are sent to a visualdisplay device as binary encoded values and stored on the display andother bits are selectively sent and used but not stored and are resentas needed. In the visual display system, some of the bits values of thepixel may be sent to the visual display device as binary encoded valuesand stored on the display, and the logical combination of other bitvalues is selectively sent to the visual display device. Selective bitsmay be logically OR'ed together and/or logically AND'ed together. Bitsmay be selected are based on zero in the current count and/or bits maybe selected based on ones in the current count.

In one embodiment, the present invention provides a digital backplanethat controls an array of processing elements wherein programmedsequence of operations is stored in memory. The locations in that memorydefine the sequence of operations to be performed by the backplane. Thesequence of operations may include controlling multiple memory pointers.The memory pointers may point at circular buffers and may share commonprocessing logic for modifying the values in the pointers. There mayalso be a set of readable and writable storage locations that containthe pointers. The program control may include values that define eitherdirectly or by computation, the starting address of one or more circularbuffers, the ending address of one or more circular buffers. Hardwaremay be used with the digital backplane, or the backplane may includehardware to modify the current value of each pointer either before orafter it is used and before it is stored back in the pointer memory. Themodification of a pointer may include incrementing to the next locationand resetting the pointer to its starting value if the value exceeds thebounds of the circular buffer. There may be redundant pointers to one ormore of the circular buffers. Also, every time a pulse width iscomputed, there are separate buffer pointers for each bit that is to beaccessed.

The sequence of operations may also repeat periodically at a rate thatis related to the line scanning rate of the display.

In the digital backplane, the process for computing the pulse width maybe changed, and the number of bits per pixel may be changed.

The digital backplane may employ a dual count process and the splitbetween which bits are treated as part of the MS-count and which bitsare treated as part of the LS-count may be changed.

In the digital backplane, data may fetched from an external memory andsends data to a display backplane in coordination with the with thequeue management on the backplane.

The controller may be on the backplane or may be external to thebackplane. The controller may do may do some processing of the databefore sending it to the backplane and the controller may perform alogical combination of bits from pixel values and then send a summarybit to be stored on the backplane. The controller may also send theaddress of where the data is to be stored on the backplane.

The control process on the backplane may also determine where theincoming data is to be stored on the backplane.

In one embodiment, the present invention provides a display processingmethod involving reading data stored on a visual display device andenabling write operations at a rate that is periodic to a multiple orsub multiple of the display refresh line rate. The sequence ofoperations may be a program stored in memory. The memory may be RAM andthe RAM may be reprogrammed. The RAM may also be reloaded while thedevice continues to operate (on-the-fly processing).

The state of processing the display processing method may include thepointer to the program location in the RAM and a variable memory thatcontains pointers to the memory buffers on the display backplane. Thetime weighting of the control pulse widths may be controlled by therelative positions of the write enable pointers. The time weighting maybe binary weighted and the time weighting may be weighted to compensatefor various desired response characteristics that may include gammacorrection and LC response. In some variations, the weighting may notrequire compensation table for the pixel values. The weighting may bedone in conjunction with compensation table(s) for the pixel values.

The bits used to compute whether or not to turn on or off a series ofpixels in a line of a visual display device may be held memory that istreated as a circular buffer. There may also be a variable number ofreads of bits required to determine the value of pixels and the sequenceof operations may reads those bits and adjusts the various pointers.

Embodiments of the present invention employ gamma correction, andmultiple time bases.

In one embodiment of the present invention, there is provided a systemfor indicating that liquid crystal materials used in the visual displaydevices, such as the visual display devices used in other embodiments ofthe present invention, have deteriorated. In many applications, suchliquid crystal materials are enclosed in a vacuum to preventdeterioration of the liquid crystal materials.

Many of the liquid crystal materials that may be used in the visualdisplay devices of the present invention include one or more esterlinkages. Examples of such liquid crystal materials are described inU.S. Pat. No. 4,695,650 and U.S. Pat. No. 5,673,028, the entiredisclosure and contents of which are hereby incorporated by reference.When such liquid crystal materials are exposed to moisture due to thevacuum environment in which they are enclosed being ruptured, hydrolysismay occur in these materials resulting in the formation of carboxylicacid groups. To detect the hydrolysis of the liquid crystal materials,various pH indicators may be used to detect the change in pH caused bythe increased presence of carboxylic acid groups.

For example, a color pH indicator may used to indicate that the liquidcrystal material has begun to deteriorate. Examples, of suitable colorpH indicators include litmus, alzarin yellow, bromcresol purple,bromocresol green, bromphenol blue, bromphenol red, bromthymol blue,cresol red, malachite green, metacresol purple, methyl orange, methylorange, methyl red, methyl-violet, orthocresol phthalein,phenolphthalein, phenol red, thymol blue, thymol phthalein, etc. Othersuitable color pH indicators are set forth in The Merck Index, 11^(th)edition, pages MISC 110-112, in The Merck Index 12^(th) edition, pagesMISC 58-60, and in U.S. Pat. No. 5,851,611 and the entire disclosure andcontents of these documents and this patent are hereby incorporated byreference. The change in color may be from one color to another, from acolor to colorless or from colorless to a color. For example,p-nitrophenol changes from yellow to colorless in the acid range andphenolphthalein changes from pink to colorless in the acid range. Also,various mixtures of color pH indicators may be used to indicate that aliquid crystal has begun to deteriorate and such mixtures allow for theuse of a spectrum of colors indicate small changes in pH.

The color pH indicator may be included in a substrate on which a liquidcrystal material is mounted, in a material protecting the liquid crystalmaterial or a material protecting the environment surrounding the liquidcrystal material. The color indicator may also be included in a strip ofmaterial that is mounted on or near the surface of the liquid crystalmaterial.

In addition to color pH indicators, the present invention may alsoemploy an electrical pH indicator. The hydrolysis of a liquid crystalmaterial may be indicated by a change in electric current, because thepresence of an acid will result in electricity being conducted better inthe hydrolyzed liquid crystal material than in the unhydrolyzed liquidcrystal material. Similarly, the presence of an acid as a decompositionproduct may be detected by a change in current.

An example of a suitable electrical pH indicator of the type that may beadapted for use in the present invention is described in U.S. Pat. No.4,618,929. Such an electrical pH indicator may include a monitoringtransducer that may be any transducer which furnishes a signal one ofwhose electrical characteristics, such as voltage, is proportional tothe measured pH. When monitoring the pH of a liquid crystal material,the transducer may include a testing pH electrode and a reference pHelectrode. The testing pH electrode may be an electrode of glass,antimony or other known type. The reference pH electrode may be anysuitable calibration electrode.

The electrical pH indicator may include an indicator visual displaydevice for providing a visual readout, such as a number or color changeindicating a pH change. The indicator display device may be mounted onthe surface of the visual display device including the liquid crystalmaterial being monitored or may be part of a monitoring system connectedto the visual display device being monitored. The electrical indicatormay also include a device for emitting a sound in the event thatdeterioration of the liquid crystal material has been detected.

The pH indicators of the present invention may be used to show anychange in the environment of the liquid crystal material that is causedby a pH change. For example, if a polymeric material is used to encloseor protect a liquid crystal material and the polymeric materialdecomposes to form an acid, such as HCl from a vinyl chloride polymer ora vinylidene chloride polymer, the pH indicator would alert the user tothe change in environment.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

What is claimed is:
 1. A device comprising: an array of light modulatingelements; and one or more processing elements for controlling each ofthe light modulating elements, wherein the light modulating elements arearranged in a two-dimensional array, and wherein the one or moreprocessing elements are adapted to skip some bit locations and use otherbit locations of bit values when performing multiple bit logical and/orarithmetic operations.
 2. The device of claim 1, wherein at least oneprocessing element of the one or more processing elements is a bitserial processing element.
 3. The device of claim 2, wherein the bitserial processing element is adapted to skip some bit locations and useother bit locations of bit values when processing a current count. 4.The device of claim 1, wherein at least one processing element of theone or more processing elements is a bit parallel processing element. 5.The device of claim 4, wherein the bit parallel processing element isadapted to skip some bit locations and use other bit locations of bitvalues when processing a current count.
 6. A device comprising: aspatial light modulator comprising a plurality of processing elementsfor computing a respective drive for each pixel of a plurality of pixelson the spatial light modulator, wherein each processing elementcomprises logic circuitry for logically and/or arithmetically comparingone or more pixel values to one or more count values, and wherein one ormore bit locations are skipped when comparing one or more pixel valuesto one or more count values.
 7. The device of claim 6, wherein theprocessing elements are bit serial processing elements.
 8. The device ofclaim 6, wherein the processing elements are bit parallel processingelements.